| 1 | /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *\ |
| 2 | * This is GNU Go, a Go program. Contact gnugo@gnu.org, or see * |
| 3 | * http://www.gnu.org/software/gnugo/ for more information. * |
| 4 | * * |
| 5 | * Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, * |
| 6 | * 2008 and 2009 by the Free Software Foundation. * |
| 7 | * * |
| 8 | * This program is free software; you can redistribute it and/or * |
| 9 | * modify it under the terms of the GNU General Public License as * |
| 10 | * published by the Free Software Foundation - version 3 or * |
| 11 | * (at your option) any later version. * |
| 12 | * * |
| 13 | * This program is distributed in the hope that it will be useful, * |
| 14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of * |
| 15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * |
| 16 | * GNU General Public License in file COPYING for more details. * |
| 17 | * * |
| 18 | * You should have received a copy of the GNU General Public * |
| 19 | * License along with this program; if not, write to the Free * |
| 20 | * Software Foundation, Inc., 51 Franklin Street, Fifth Floor, * |
| 21 | * Boston, MA 02111, USA. * |
| 22 | \* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */ |
| 23 | |
| 24 | #include "gnugo.h" |
| 25 | |
| 26 | #include <stdio.h> |
| 27 | #include <string.h> |
| 28 | #include <stdlib.h> |
| 29 | |
| 30 | #include "liberty.h" |
| 31 | |
| 32 | /* Capture as many strings of the given color as we can. Played stones |
| 33 | * are left on the board and the number of played stones is returned. |
| 34 | * Strings marked in the exceptions array are excluded from capturing |
| 35 | * attempts. If all non-excepted strings are successfully captured, |
| 36 | * *none_invincible is set to one. Set none_invincible to NULL if you |
| 37 | * don't need that information. |
| 38 | */ |
| 39 | static int |
| 40 | capture_non_invincible_strings(int color, int exceptions[BOARDMAX], |
| 41 | int *none_invincible) |
| 42 | { |
| 43 | int other = OTHER_COLOR(color); |
| 44 | int something_captured = 1; /* To get into the first turn of the loop. */ |
| 45 | int string_found = 0; |
| 46 | int moves_played = 0; |
| 47 | int save_moves; |
| 48 | int libs[MAXLIBS]; |
| 49 | int liberties; |
| 50 | int pos; |
| 51 | int k; |
| 52 | |
| 53 | while (something_captured) { |
| 54 | /* Nothing captured so far in this turn of the loop. */ |
| 55 | something_captured = 0; |
| 56 | |
| 57 | /* Is there something left to try to capture? */ |
| 58 | string_found = 0; |
| 59 | |
| 60 | /* Visit all friendly strings on the board. */ |
| 61 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 62 | if (board[pos] != color || find_origin(pos) != pos) |
| 63 | continue; |
| 64 | |
| 65 | if (exceptions && exceptions[pos]) |
| 66 | continue; |
| 67 | |
| 68 | string_found = 1; |
| 69 | |
| 70 | /* Try to capture the string at pos. */ |
| 71 | liberties = findlib(pos, MAXLIBS, libs); |
| 72 | save_moves = moves_played; |
| 73 | for (k = 0; k < liberties; k++) { |
| 74 | if (trymove(libs[k], other, "unconditional_life", pos)) |
| 75 | moves_played++; |
| 76 | } |
| 77 | |
| 78 | /* Successful if already captured or a single liberty remains. |
| 79 | * Otherwise we must rewind and take back the last batch of moves. |
| 80 | */ |
| 81 | if (board[pos] == EMPTY) |
| 82 | something_captured = 1; |
| 83 | else if (findlib(pos, 2, libs) == 1) { |
| 84 | /* Need to use tryko as a defense against the extreme case |
| 85 | * when the only opponent liberty that is not suicide is an |
| 86 | * illegal ko capture, like in this 5x5 position: |
| 87 | * +-----+ |
| 88 | * |.XO.O| |
| 89 | * |XXOO.| |
| 90 | * |X.XOO| |
| 91 | * |XXOO.| |
| 92 | * |.XO.O| |
| 93 | * +-----+ |
| 94 | */ |
| 95 | int success = tryko(libs[0], other, "unconditional_life"); |
| 96 | gg_assert(success); |
| 97 | moves_played++; |
| 98 | something_captured = 1; |
| 99 | } |
| 100 | else |
| 101 | while (moves_played > save_moves) { |
| 102 | popgo(); |
| 103 | moves_played--; |
| 104 | } |
| 105 | } |
| 106 | } |
| 107 | |
| 108 | if (none_invincible) |
| 109 | *none_invincible = !string_found; |
| 110 | |
| 111 | return moves_played; |
| 112 | } |
| 113 | |
| 114 | /* Find those worms of the given color that can never be captured, |
| 115 | * even if the opponent is allowed an arbitrary number of consecutive |
| 116 | * moves. The coordinates of the origins of these worms are written to |
| 117 | * the worm arrays and the number of non-capturable worms is |
| 118 | * returned. |
| 119 | * |
| 120 | * The algorithm is to cycle through the worms until none remains or |
| 121 | * no more can be captured. A worm is removed when it is found to be |
| 122 | * capturable, by letting the opponent try to play on all its |
| 123 | * liberties. If the attack fails, the moves are undone. When no more |
| 124 | * worm can be removed in this way, the remaining ones are |
| 125 | * unconditionally alive. |
| 126 | * |
| 127 | * After this, unconditionally dead opponent worms and unconditional |
| 128 | * territory are identified. This is almost, but only almost, |
| 129 | * straightforward. We first present a simple but only almost correct |
| 130 | * solution, then show how to patch up its deficiencies. |
| 131 | * |
| 132 | * - - - - - - - |
| 133 | * |
| 134 | * Algorithm 1, simple but slightly incorrect. |
| 135 | * |
| 136 | * To find unconditionally dead opponent worms and unconditional |
| 137 | * territory, we continue from the position obtained at the end of the |
| 138 | * previous operation (only unconditionally alive strings remain for |
| 139 | * color) with the following steps: |
| 140 | * |
| 141 | * 1. Play opponent stones on all liberties of the unconditionally |
| 142 | * alive strings except where illegal. (That the move order may |
| 143 | * determine exactly which liberties can be played legally is not |
| 144 | * important. Just pick an arbitrary order). |
| 145 | * 2. Recursively extend opponent strings in atari, except where this |
| 146 | * would be suicide. |
| 147 | * 3. Play an opponent stone anywhere it can get two empty |
| 148 | * neighbors. (I.e. split big eyes into small ones). |
| 149 | * 4. Play an opponent stone anywhere it can get one empty |
| 150 | * neighbor. (I.e. reduce two space eyes to one space eyes.) |
| 151 | * |
| 152 | * Remaining opponent strings in atari and remaining liberties of the |
| 153 | * unconditionally alive strings constitute the unconditional |
| 154 | * territory. |
| 155 | * |
| 156 | * Opponent strings from the initial position placed on |
| 157 | * unconditional territory are unconditionally dead. |
| 158 | * |
| 159 | * - - - - - - - |
| 160 | * |
| 161 | * The deficiency with this algorithm is that a certain class of sekis |
| 162 | * are considered as dead, e.g. this position: |
| 163 | * |
| 164 | * .OOOOO. |
| 165 | * OOXXXOO |
| 166 | * OXX.XXO |
| 167 | * OX.O.XO |
| 168 | * OX.O.XO |
| 169 | * OXX.XXO |
| 170 | * OOXXXOO |
| 171 | * .OOOOO. |
| 172 | * |
| 173 | * The problem is that while removing the two O stones, X is reduced |
| 174 | * to a single small eye. Still O cannot capture these stones under |
| 175 | * alternating play since the eyespace is too big. |
| 176 | * |
| 177 | * Before discussing this seki further we make a preliminary |
| 178 | * modification of the algorithm. |
| 179 | * |
| 180 | * - - - - - - - |
| 181 | * |
| 182 | * Algorithm 2. More complex but still slightly incorrect algorithm: |
| 183 | * |
| 184 | * 1. Run algorithm 1. |
| 185 | * 2. Return to the original position. |
| 186 | * 3. Capture all capturable O strings which according to algorithm 1 |
| 187 | * do not belong to unconditional territory. |
| 188 | * 4. Play opponent stones on all liberties of the unconditionally |
| 189 | * alive strings except where illegal. (That the move order may |
| 190 | * determine exactly which liberties can be played legally is not |
| 191 | * important. Just pick an arbitrary order). |
| 192 | * 5. Recursively extend opponent strings in atari, except where this |
| 193 | * would be suicide. |
| 194 | * 6. Capture all remaining capturable O strings. |
| 195 | * 7. Repeat 4 and 5 once. |
| 196 | * 8. Play an opponent stone anywhere it can get two empty |
| 197 | * neighbors. (I.e. split big eyes into small ones). |
| 198 | * 9. Play an opponent stone anywhere it can get one empty |
| 199 | * neighbor. (I.e. reduce two space eyes to one space eyes.) |
| 200 | * |
| 201 | * Remaining opponent strings in atari and remaining liberties of the |
| 202 | * unconditionally alive strings constitute the unconditional |
| 203 | * territory. |
| 204 | * |
| 205 | * Opponent strings from the initial position placed on |
| 206 | * unconditional territory are unconditionally dead. |
| 207 | * |
| 208 | * - - - - - - - |
| 209 | * |
| 210 | * We can observe that, after step 5, an X group with at least two |
| 211 | * distinct eyespaces would not risk being reduced to a single small |
| 212 | * eye. Similarly an X group with a capturable O string of size at |
| 213 | * least three would allow the formation of two distinct small eyes |
| 214 | * after being captured. Thus it is easy to see that the only X groups |
| 215 | * which would live in seki but could not be transformed into |
| 216 | * unconditionally alive groups would have a single eyespace with a |
| 217 | * capturable O string of size at most 2. Furthermore the eyespace |
| 218 | * would not be possible to subdivide. Then if the capturable string |
| 219 | * would be of size 1 it would in all cases form a nakade and we would |
| 220 | * not have a seki. The plausible seki positions would all be |
| 221 | * reducable to the following eyeshape: |
| 222 | * |
| 223 | * .OOOOO. |
| 224 | * OOXXXO. |
| 225 | * OXX.XOO |
| 226 | * OX.OXXO |
| 227 | * OXXO.XO |
| 228 | * OOX.XXO |
| 229 | * .OXXXOO |
| 230 | * .OOOOO. |
| 231 | * |
| 232 | * The remaining question is what effects cutting points in the X |
| 233 | * group would have. For example these X groups are dead: |
| 234 | * |
| 235 | * .OOOOO. .OOOOO. .OOOOO. .OOOOO. ..OOOO. ..OOOO. |
| 236 | * .OXXXO. .OXXXO. .OXXXO. .OXXXO. OOOXXO. OOOXXO. |
| 237 | * OOX.XO. OOX.XOO OOX.XOO OOX.XOO OXX.XO. OXX.XOO |
| 238 | * OX.OXOO OX.OXXO OX.OXXO OX.OXXO OX.OXOO OX.OXXO |
| 239 | * OXXO.XO OXXO.XO OXXO.XO OXXO.XO OXXO.XO OXXO.XO |
| 240 | * OOX.XXO OOX.XOO OOX.XXO OOX.XXO OOX.XXO OOX.XXO |
| 241 | * .OXXXOO .OXXXO. .OXXOOO .OOXXOO .OXXXOO .OXXOOO |
| 242 | * .OOOOO. .OOOOO. .OOOO.. ..OOOO. .OOOOO. .OOOO.. |
| 243 | * |
| 244 | * while these are alive in seki |
| 245 | * |
| 246 | * ..OOOO. .OOOO.. .OOOO.. ..OOOO. ..OOOO. |
| 247 | * OOOXXO. .OXXOO. OOXXOO. .OOXXO. OOOXXO. |
| 248 | * OXX.XOO OOX.XOO OXX.XOO OOX.XOO OXX.XOO |
| 249 | * OX.OXXO OX.OXXO OX.OXXO OX.OXXO OX.OXXO |
| 250 | * OXXO.XO OXXO.XO OOXO.XO OXXO.XO OOXO.XO |
| 251 | * OOX.XXO OOX.XXO .OX.XXO OOX.XXO .OX.XXO |
| 252 | * .OXXXOO .OXXXOO .OXXOOO .OXXXOO .OXXXOO |
| 253 | * .OOOOO. .OOOOO. .OOOO.. ..OOOO. .OOOOO. |
| 254 | * |
| 255 | * The critical distinction between the dead ones and the seki ones is |
| 256 | * that the stones marked a and b below, |
| 257 | * |
| 258 | * .OOOOO. |
| 259 | * OOXXXO. |
| 260 | * OXX.XOO |
| 261 | * OX.ObXO |
| 262 | * OXaO.XO |
| 263 | * OOX.XXO |
| 264 | * .OXXXOO |
| 265 | * .OOOOO. |
| 266 | * |
| 267 | * belong to different strings for the dead groups and to the same |
| 268 | * string for the seki groups. |
| 269 | * |
| 270 | * The trick to avoid misclassifying areas where the opponent can form |
| 271 | * a seki group but not an invincible group as unconditional territory |
| 272 | * is thus to detect the formation above and add a third stone to the |
| 273 | * O group before the capturing in step 6 above. |
| 274 | * |
| 275 | * This leads to the final algorithm. |
| 276 | * |
| 277 | * - - - - - - - |
| 278 | * |
| 279 | * Algorithm 3. Final and correct algorithm: |
| 280 | * |
| 281 | * 1. Run algorithm 1. |
| 282 | * 2. Return to the original position. |
| 283 | * 3. Capture all capturable O strings which according to algorithm 1 |
| 284 | * do not belong to unconditional territory. |
| 285 | * 4. Play opponent stones on all liberties of the unconditionally |
| 286 | * alive strings except where illegal. (That the move order may |
| 287 | * determine exactly which liberties can be played legally is not |
| 288 | * important. Just pick an arbitrary order). |
| 289 | * 5. Recursively extend opponent strings in atari, except where this |
| 290 | * would be suicide. |
| 291 | * 6. Identify eyespaces of the kind described above and extend any |
| 292 | * matching two-stone string with a third stone. |
| 293 | * 7. Capture all remaining capturable O strings. |
| 294 | * 8. Repeat 4 and 5 once. |
| 295 | * 9. Play an opponent stone anywhere it can get two empty |
| 296 | * neighbors. (I.e. split big eyes into small ones). |
| 297 | * 10. Play an opponent stone anywhere it can get one empty |
| 298 | * neighbor. (I.e. reduce two space eyes to one space eyes.) |
| 299 | * |
| 300 | * Remaining opponent strings in atari and remaining liberties of the |
| 301 | * unconditionally alive strings constitute the unconditional |
| 302 | * territory. |
| 303 | * |
| 304 | * Opponent strings from the initial position placed on |
| 305 | * unconditional territory are unconditionally dead. |
| 306 | * |
| 307 | * - - - - - - - |
| 308 | * |
| 309 | * On return, unconditional_territory[][] is 1 where color has |
| 310 | * unconditionally alive stones, 2 where it has unconditional |
| 311 | * territory, and 0 otherwise. |
| 312 | */ |
| 313 | |
| 314 | void |
| 315 | unconditional_life(int unconditional_territory[BOARDMAX], int color) |
| 316 | { |
| 317 | int found_one; |
| 318 | int other = OTHER_COLOR(color); |
| 319 | int libs[MAXLIBS]; |
| 320 | int liberties; |
| 321 | int pos; |
| 322 | int k, r; |
| 323 | int moves_played; |
| 324 | int potential_sekis[BOARDMAX]; |
| 325 | int none_invincible; |
| 326 | |
| 327 | /* Initialize unconditional_territory array. */ |
| 328 | memset(unconditional_territory, 0, |
| 329 | sizeof(unconditional_territory[0]) * BOARDMAX); |
| 330 | |
| 331 | /* Find isolated two-stone strings which might be involved in the |
| 332 | * kind of seki described in the comments. |
| 333 | */ |
| 334 | memset(potential_sekis, 0, sizeof(potential_sekis)); |
| 335 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 336 | int isolated = 1; |
| 337 | int stones[2]; |
| 338 | int pos2; |
| 339 | |
| 340 | if (board[pos] != color |
| 341 | || find_origin(pos) != pos |
| 342 | || countstones(pos) != 2) |
| 343 | continue; |
| 344 | |
| 345 | findstones(pos, 2, stones); |
| 346 | for (k = 0; k < 2 && isolated; k++) { |
| 347 | for (r = 0; r < 8 && isolated; r++) { |
| 348 | pos2 = stones[k] + delta[r]; |
| 349 | if (!ON_BOARD(pos2) |
| 350 | || (board[pos2] == color |
| 351 | && !same_string(pos, pos2))) |
| 352 | isolated = 0; |
| 353 | } |
| 354 | } |
| 355 | |
| 356 | if (isolated) { |
| 357 | potential_sekis[stones[0]] = 1; |
| 358 | potential_sekis[stones[1]] = 1; |
| 359 | } |
| 360 | } |
| 361 | |
| 362 | moves_played = capture_non_invincible_strings(color, potential_sekis, |
| 363 | &none_invincible); |
| 364 | |
| 365 | /* If there are no invincible strings, nothing can be unconditionally |
| 366 | * settled. |
| 367 | */ |
| 368 | if (none_invincible) { |
| 369 | /* Take back all moves. */ |
| 370 | while (moves_played > 0) { |
| 371 | popgo(); |
| 372 | moves_played--; |
| 373 | } |
| 374 | return; |
| 375 | } |
| 376 | |
| 377 | /* The strings still remaining except those marked in |
| 378 | * potential_sekis[] are uncapturable. Now see which opponent |
| 379 | * strings can survive. |
| 380 | * |
| 381 | * 1. Play opponent stones on all liberties of the unconditionally |
| 382 | * alive strings except where illegal. |
| 383 | */ |
| 384 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 385 | if (board[pos] != color || potential_sekis[pos] || find_origin(pos) != pos) |
| 386 | continue; |
| 387 | |
| 388 | /* Play as many liberties as we can. */ |
| 389 | liberties = findlib(pos, MAXLIBS, libs); |
| 390 | for (k = 0; k < liberties; k++) { |
| 391 | if (trymove(libs[k], other, "unconditional_life", pos)) |
| 392 | moves_played++; |
| 393 | } |
| 394 | } |
| 395 | |
| 396 | /* 2. Recursively extend opponent strings in atari, except where this |
| 397 | * would be suicide. |
| 398 | */ |
| 399 | found_one = 1; |
| 400 | while (found_one) { |
| 401 | /* Nothing found so far in this turn of the loop. */ |
| 402 | found_one = 0; |
| 403 | |
| 404 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 405 | if (board[pos] != other || countlib(pos) > 1) |
| 406 | continue; |
| 407 | |
| 408 | /* Try to extend the string at (m, n). */ |
| 409 | findlib(pos, 1, libs); |
| 410 | if (trymove(libs[0], other, "unconditional_life", pos)) { |
| 411 | moves_played++; |
| 412 | found_one = 1; |
| 413 | } |
| 414 | } |
| 415 | } |
| 416 | |
| 417 | /* Now see whether there are any significant sekis on the board. */ |
| 418 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 419 | if (!potential_sekis[pos] |
| 420 | || board[pos] == EMPTY |
| 421 | || find_origin(pos) != pos) |
| 422 | continue; |
| 423 | for (r = 0; r < 4; r++) { |
| 424 | int up = delta[r]; |
| 425 | int right = delta[(r + 1) % 4]; |
| 426 | int locally_played_moves = 0; |
| 427 | if (board[pos + up] != color |
| 428 | || board[pos + up + up] != EMPTY |
| 429 | || board[pos - up] != EMPTY) |
| 430 | continue; |
| 431 | for (k = 0; k < 2; k++) { |
| 432 | if (k == 1) |
| 433 | right = -right; |
| 434 | if (board[pos + right] != EMPTY || board[pos + up - right] != EMPTY) |
| 435 | continue; |
| 436 | if (board[pos - right] == EMPTY |
| 437 | && trymove(pos - right, other, "unconditional_life", pos)) |
| 438 | locally_played_moves++; |
| 439 | if (board[pos + up + right] == EMPTY |
| 440 | && trymove(pos + up + right, other, "unconditional_life", pos)) |
| 441 | locally_played_moves++; |
| 442 | if (board[pos - right] == other && board[pos + up + right] == other |
| 443 | && same_string(pos - right, pos + up + right)) { |
| 444 | /* This is a critical seki. Extend the string with one stone |
| 445 | * in an arbitrary direction to break the seki. |
| 446 | */ |
| 447 | while (locally_played_moves > 0) { |
| 448 | popgo(); |
| 449 | locally_played_moves--; |
| 450 | } |
| 451 | trymove(pos - up, color, "unconditional_life", pos); |
| 452 | moves_played++; |
| 453 | break; |
| 454 | } |
| 455 | else { |
| 456 | while (locally_played_moves > 0) { |
| 457 | popgo(); |
| 458 | locally_played_moves--; |
| 459 | } |
| 460 | } |
| 461 | } |
| 462 | if (countstones(pos) > 2) |
| 463 | break; |
| 464 | } |
| 465 | } |
| 466 | |
| 467 | /* Capture the strings involved in potential sekis. */ |
| 468 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 469 | if (!potential_sekis[pos] || board[pos] == EMPTY) |
| 470 | continue; |
| 471 | /* Play as many liberties as we can. */ |
| 472 | liberties = findlib(pos, MAXLIBS, libs); |
| 473 | for (k = 0; k < liberties; k++) { |
| 474 | if (trymove(libs[k], other, "unconditional_life", pos)) |
| 475 | moves_played++; |
| 476 | } |
| 477 | } |
| 478 | |
| 479 | |
| 480 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 481 | int apos; |
| 482 | int bpos; |
| 483 | int aopen, bopen; |
| 484 | int alib, blib; |
| 485 | if (board[pos] != other || countlib(pos) != 2) |
| 486 | continue; |
| 487 | findlib(pos, 2, libs); |
| 488 | apos = libs[0]; |
| 489 | bpos = libs[1]; |
| 490 | if (abs(I(apos) - I(bpos)) + abs(J(apos) - J(bpos)) != 1) |
| 491 | continue; |
| 492 | |
| 493 | /* Only two liberties and these are adjacent. Play one. We want |
| 494 | * to maximize the number of open liberties. In this particular |
| 495 | * situation we can count this with approxlib for the opposite |
| 496 | * color. If the number of open liberties is the same, we |
| 497 | * maximize the total number of obtained liberties. |
| 498 | * Two relevant positions: |
| 499 | * |
| 500 | * |XXX. |
| 501 | * |OOXX |XXXXXXX |
| 502 | * |O.OX |OOXOOOX |
| 503 | * |..OX |..OO.OX |
| 504 | * +---- +------- |
| 505 | */ |
| 506 | aopen = approxlib(apos, color, 4, NULL); |
| 507 | bopen = approxlib(bpos, color, 4, NULL); |
| 508 | alib = approxlib(apos, other, 4, NULL); |
| 509 | blib = approxlib(bpos, other, 4, NULL); |
| 510 | |
| 511 | if (aopen > bopen || (aopen == bopen && alib >= blib)) { |
| 512 | trymove(apos, other, "unconditional_life", pos); |
| 513 | moves_played++; |
| 514 | } |
| 515 | else { |
| 516 | trymove(bpos, other, "unconditional_life", pos); |
| 517 | moves_played++; |
| 518 | } |
| 519 | } |
| 520 | |
| 521 | /* Identify unconditionally alive stones and unconditional territory. */ |
| 522 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 523 | if (board[pos] == color && !potential_sekis[pos]) { |
| 524 | unconditional_territory[pos] = 1; |
| 525 | if (find_origin(pos) == pos) { |
| 526 | liberties = findlib(pos, MAXLIBS, libs); |
| 527 | for (k = 0; k < liberties; k++) |
| 528 | unconditional_territory[libs[k]] = 2; |
| 529 | } |
| 530 | } |
| 531 | else if (board[pos] == other && countlib(pos) == 1) { |
| 532 | unconditional_territory[pos] = 2; |
| 533 | findlib(pos, 1, libs); |
| 534 | unconditional_territory[libs[0]] = 2; |
| 535 | } |
| 536 | } |
| 537 | |
| 538 | /* Take back all moves. */ |
| 539 | while (moves_played > 0) { |
| 540 | popgo(); |
| 541 | moves_played--; |
| 542 | } |
| 543 | } |
| 544 | |
| 545 | |
| 546 | /* By unconditional status analysis we can statically find some moves |
| 547 | * which there is never any need to play. Those belong to three |
| 548 | * different categories: |
| 549 | * |
| 550 | * 1. A move on a vertex which is already unconditional territory for |
| 551 | * either color. |
| 552 | * 2. A move which after having been made ends up as unconditional |
| 553 | * territory for the opponent. |
| 554 | * 3. If a move at vertex A makes vertex B become unconditional |
| 555 | * territory, there is no need to consider a move at B, since A has |
| 556 | * all the positive effects that B would have. |
| 557 | * |
| 558 | * Moves in categories 1 and 2 are never any better than passing and |
| 559 | * often worse (with territory scoring always worse). Moves in |
| 560 | * category three can be either better or worse than passing, but it's |
| 561 | * always true that a move at A is at least as good as a move at B. |
| 562 | * Occasionally they are identically good (A makes B unconditional |
| 563 | * territory and B makes A unconditional territory) but there is never |
| 564 | * any need to analyze both. |
| 565 | * |
| 566 | * In meaningless_black_moves[] and meaningless_white_moves[] a value |
| 567 | * of -1 means it is not meaningless, 0 (NO_MOVE) means it belongs to |
| 568 | * category 1 or 2, and a value greater than zero points to the |
| 569 | * preferred move in category 3. |
| 570 | * |
| 571 | * The parameter unconditional_territory should contain the result of |
| 572 | * calling unconditional_life() in the original position. Meaningless |
| 573 | * moves are computed for the given color. |
| 574 | */ |
| 575 | void |
| 576 | find_unconditionally_meaningless_moves(int unconditional_territory[BOARDMAX], |
| 577 | int color) |
| 578 | { |
| 579 | int *meaningless_moves; |
| 580 | int other = OTHER_COLOR(color); |
| 581 | int friendly_unconditional[BOARDMAX]; |
| 582 | int opponent_unconditional[BOARDMAX]; |
| 583 | int pos; |
| 584 | int pos2; |
| 585 | |
| 586 | gg_assert(color == BLACK || color == WHITE); |
| 587 | |
| 588 | if (color == BLACK) |
| 589 | meaningless_moves = meaningless_black_moves; |
| 590 | else |
| 591 | meaningless_moves = meaningless_white_moves; |
| 592 | |
| 593 | /* Initialize meaningless_moves and detect moves of category 1, but |
| 594 | * only for own unconditional territory. |
| 595 | * |
| 596 | * FIXME: We would save some time by detecting all category 1 moves |
| 597 | * here but then we would need to have the initial unconditional |
| 598 | * territory for the opponent as well. This can of course be done, |
| 599 | * the question is how we get it in the nicest way. |
| 600 | */ |
| 601 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) |
| 602 | if (board[pos] == EMPTY) { |
| 603 | if (unconditional_territory[pos]) |
| 604 | meaningless_moves[pos] = NO_MOVE; |
| 605 | else |
| 606 | meaningless_moves[pos] = -1; |
| 607 | } |
| 608 | |
| 609 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { |
| 610 | if (board[pos] != EMPTY || meaningless_moves[pos] != -1) |
| 611 | continue; |
| 612 | |
| 613 | if (!tryko(pos, color, "find_unconditionally_meaningless_moves")) |
| 614 | continue; |
| 615 | |
| 616 | unconditional_life(opponent_unconditional, other); |
| 617 | if (opponent_unconditional[pos]) { |
| 618 | /* Move of category 1 or 2. */ |
| 619 | meaningless_moves[pos] = NO_MOVE; |
| 620 | } |
| 621 | else { |
| 622 | unconditional_life(friendly_unconditional, color); |
| 623 | if (friendly_unconditional[pos]) |
| 624 | for (pos2 = BOARDMIN; pos2 < BOARDMAX; pos2++) |
| 625 | if (board[pos2] == EMPTY |
| 626 | && meaningless_moves[pos2] == -1 |
| 627 | && friendly_unconditional[pos2]) { |
| 628 | /* Move of category 3. */ |
| 629 | meaningless_moves[pos2] = pos; |
| 630 | } |
| 631 | } |
| 632 | |
| 633 | popgo(); |
| 634 | } |
| 635 | |
| 636 | /* Meaningless moves of category 3 may have been found in multiple |
| 637 | * steps. Normalize to the final replacement move. |
| 638 | */ |
| 639 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) |
| 640 | if (board[pos] == EMPTY && meaningless_moves[pos] > 0) |
| 641 | while (meaningless_moves[meaningless_moves[pos]] > 0) |
| 642 | meaningless_moves[pos] = meaningless_moves[meaningless_moves[pos]]; |
| 643 | } |
| 644 | |
| 645 | /* Returns 1 if the move at pos by color is meaningless and 0 |
| 646 | * otherwise. When it is meaningless, *replacement_move will contain a |
| 647 | * replacing move, which is NO_MOVE if passing is guaranteed to be no |
| 648 | * worse than making the move. |
| 649 | */ |
| 650 | int |
| 651 | unconditionally_meaningless_move(int pos, int color, int *replacement_move) |
| 652 | { |
| 653 | if (color == WHITE && meaningless_white_moves[pos] != -1) { |
| 654 | *replacement_move = meaningless_white_moves[pos]; |
| 655 | return 1; |
| 656 | } |
| 657 | if (color == BLACK && meaningless_black_moves[pos] != -1) { |
| 658 | *replacement_move = meaningless_black_moves[pos]; |
| 659 | return 1; |
| 660 | } |
| 661 | |
| 662 | return 0; |
| 663 | } |
| 664 | |
| 665 | void |
| 666 | clear_unconditionally_meaningless_moves() |
| 667 | { |
| 668 | int pos; |
| 669 | |
| 670 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) |
| 671 | if (ON_BOARD(pos)) { |
| 672 | meaningless_black_moves[pos] = -1; |
| 673 | meaningless_white_moves[pos] = -1; |
| 674 | } |
| 675 | } |
| 676 | |
| 677 | /* Pick up antisuji and replacement move reasons found by analysis |
| 678 | * of unconditional status. |
| 679 | */ |
| 680 | void |
| 681 | unconditional_move_reasons(int color) |
| 682 | { |
| 683 | int replacement_move; |
| 684 | int pos; |
| 685 | |
| 686 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) |
| 687 | if (board[pos] == EMPTY |
| 688 | && unconditionally_meaningless_move(pos, color, &replacement_move)) { |
| 689 | if (replacement_move == NO_MOVE) { |
| 690 | TRACE("%1m unconditional antisuji.\n", pos); |
| 691 | add_antisuji_move(pos); |
| 692 | } |
| 693 | else { |
| 694 | TRACE("%1m unconditionally replaced to %1m.\n", pos, replacement_move); |
| 695 | add_replacement_move(pos, replacement_move, color); |
| 696 | } |
| 697 | } |
| 698 | } |
| 699 | |
| 700 | /* |
| 701 | * Local Variables: |
| 702 | * tab-width: 8 |
| 703 | * c-basic-offset: 2 |
| 704 | * End: |
| 705 | */ |