tactics/2lib.c

   1 #include <assert.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4
   5 #define DEBUG
   6 #include "board.h"
   7 #include "debug.h"
   8 #include "mq.h"
   9 #include "tactics/2lib.h"
  10 #include "tactics/selfatari.h"
  11
  12
  13 /* Whether to avoid capturing/atariing doomed groups (this is big
  14  * performance hit and may reduce playouts balance; it does increase
  15  * the strength, but not quite proportionally to the performance). */
  16 //#define NO_DOOMED_GROUPS
  17
  18
  19 static bool
  20 miai_2lib(struct board *b, group_t group, enum stone color)
  21 {
  22         bool can_connect = false, can_pull_out = false;
  23         /* We have miai if we can either connect on both libs,
  24          * or connect on one lib and escape on another. (Just
  25          * having two escape routes can be risky.) We must make
  26          * sure that we don't consider following as miai:
  27          * X X X O
  28          * X . . O
  29          * O O X O - left dot would be pull-out, right dot connect */
  30         foreach_neighbor(b, board_group_info(b, group).lib[0], {
  31                 enum stone cc = board_at(b, c);
  32                 if (cc == S_NONE && cc != board_at(b, board_group_info(b, group).lib[1])) {
  33                         can_pull_out = true;
  34                 } else if (cc != color) {
  35                         continue;
  36                 }
  37
  38                 group_t cg = group_at(b, c);
  39                 if (cg && cg != group && board_group_info(b, cg).libs > 1)
  40                         can_connect = true;
  41         });
  42         foreach_neighbor(b, board_group_info(b, group).lib[1], {
  43                 enum stone cc = board_at(b, c);
  44                 if (c == board_group_info(b, group).lib[0])
  45                         continue;
  46                 if (cc == S_NONE && can_connect) {
  47                         return true;
  48                 } else if (cc != color) {
  49                         continue;
  50                 }
  51
  52                 group_t cg = group_at(b, c);
  53                 if (cg && cg != group && board_group_info(b, cg).libs > 1)
  54                         return (can_connect || can_pull_out);
  55         });
  56         return false;
  57 }
  58
  59 static bool
  60 defense_is_hopeless(struct board *b, group_t group, enum stone owner,
  61                         enum stone to_play, coord_t lib, coord_t otherlib,
  62                         bool use)
  63 {
  64         /* If we are the defender not connecting out, do not
  65          * escape with moves that do not gain liberties anyway
  66          * - either the new extension has just single extra
  67          * liberty, or the "gained" liberties are shared. */
  68         /* XXX: We do not check connecting to a short-on-liberty
  69          * group (e.g. ourselves). */
  70         if (DEBUGL(7))
  71                 fprintf(stderr, "\tif_check %d and defending %d and uscount %d ilcount %d\n",
  72                         use, to_play == owner,
  73                         neighbor_count_at(b, lib, owner),
  74                         immediate_liberty_count(b, lib));
  75         if (!use)
  76                 return false;
  77         if (to_play == owner && neighbor_count_at(b, lib, owner) == 1) {
  78                 if (immediate_liberty_count(b, lib) == 1)
  79                         return true;
  80                 if (immediate_liberty_count(b, lib) == 2
  81                     && coord_is_adjecent(lib, otherlib, b))
  82                         return true;
  83         }
  84         return false;
  85 }
  86
  87 void
  88 can_atari_group(struct board *b, group_t group, enum stone owner,
  89                   enum stone to_play, struct move_queue *q,
  90                   int tag, bool use_def_no_hopeless)
  91 {
  92         bool have[2] = { false, false };
  93         bool preference[2] = { true, true };
  94         for (int i = 0; i < 2; i++) {
  95                 coord_t lib = board_group_info(b, group).lib[i];
  96                 assert(board_at(b, lib) == S_NONE);
  97                 if (!board_is_valid_play(b, to_play, lib))
  98                         continue;
  99
 100                 if (DEBUGL(6))
 101                         fprintf(stderr, "- checking liberty %s of %s %s, filled by %s\n",
 102                                 coord2sstr(lib, b),
 103                                 stone2str(owner), coord2sstr(group, b),
 104                                 stone2str(to_play));
 105
 106                 /* Don't play at the spot if it is extremely short
 107                  * of liberties... */
 108                 /* XXX: This looks harmful, could significantly
 109                  * prefer atari to throwin:
 110                  *
 111                  * XXXOOOOOXX
 112                  * .OO.....OX
 113                  * XXXOOOOOOX */
 114 #if 0
 115                 if (neighbor_count_at(b, lib, stone_other(owner)) + immediate_liberty_count(b, lib) < 2)
 116                         continue;
 117 #endif
 118
 119                 /* Prevent hopeless escape attempts. */
 120                 if (defense_is_hopeless(b, group, owner, to_play, lib,
 121                                         board_group_info(b, group).lib[1 - i],
 122                                         use_def_no_hopeless))
 123                         continue;
 124
 125 #ifdef NO_DOOMED_GROUPS
 126                 /* If the owner can't play at the spot, we don't want
 127                  * to bother either. */
 128                 if (is_bad_selfatari(b, owner, lib))
 129                         continue;
 130 #endif
 131
 132                 /* Of course we don't want to play bad selfatari
 133                  * ourselves, if we are the attacker... */
 134                 if (
 135 #ifdef NO_DOOMED_GROUPS
 136                     to_play != owner &&
 137 #endif
 138                     is_bad_selfatari(b, to_play, lib)) {
 139                         if (DEBUGL(7))
 140                                 fprintf(stderr, "\tliberty is selfatari\n");
 141                         coord_t coord = pass;
 142                         if (to_play != owner) {
 143                                 /* Okay! We are attacker; maybe we just need
 144                                  * to connect a false eye before atari - this
 145                                  * is very common in the corner. */
 146                                 coord = selfatari_cousin(b, to_play, lib, NULL);
 147                         }
 148                         if (is_pass(coord))
 149                                 continue;
 150                         /* Ok, connect, but prefer not to. */
 151                         if (DEBUGL(7))
 152                                 fprintf(stderr, "\treluctantly switching to cousin %s\n", coord2sstr(coord, b)),
 153                         lib = coord;
 154                         preference[i] = false;
 155
 156                 /* By now, we must be decided we add the move to the
 157                  * queue!  [comment intentionally misindented] */
 158
 159                 }
 160
 161                 have[i] = true;
 162
 163                 /* If the move is too "lumpy", prefer the alternative:
 164                  *
 165                  * #######
 166                  * ..O.X.X <- always play the left one!
 167                  * OXXXXXX */
 168                 if (neighbor_count_at(b, lib, to_play) + neighbor_count_at(b, lib, S_OFFBOARD) >= 3) {
 169                         if (DEBUGL(7))
 170                                 fprintf(stderr, "\tlumpy: mine %d + edge %d\n",
 171                                         neighbor_count_at(b, lib, to_play),
 172                                         neighbor_count_at(b, lib, S_OFFBOARD));
 173                         preference[i] = false;
 174                 }
 175
 176                 if (DEBUGL(6))
 177                         fprintf(stderr, "+ liberty %s ready with preference %d\n", coord2sstr(lib, b), preference[i]);
 178
 179                 /* If we prefer only one of the moves, pick that one. */
 180                 if (i == 1 && have[0] && preference[0] != preference[1]) {
 181                         if (!preference[0]) {
 182                                 if (q->move[q->moves - 1] == board_group_info(b, group).lib[0])
 183                                         q->moves--;
 184                                 /* ...else{ may happen, since we call
 185                                  * mq_nodup() and the move might have
 186                                  * been there earlier. */
 187                         } else {
 188                                 assert(!preference[1]);
 189                                 continue;
 190                         }
 191                 }
 192
 193                 /* Tasty! Crispy! Good! */
 194                 mq_add(q, lib, tag);
 195                 mq_nodup(q);
 196         }
 197
 198         if (DEBUGL(7)) {
 199                 char label[256];
 200                 snprintf(label, 256, "= final %s %s liberties to play by %s",
 201                         stone2str(owner), coord2sstr(group, b),
 202                         stone2str(to_play));
 203                 mq_print(q, b, label);
 204         }
 205 }
 206
 207 void
 208 group_2lib_check(struct board *b, group_t group, enum stone to_play, struct move_queue *q, int tag, bool use_miaisafe, bool use_def_no_hopeless)
 209 {
 210         enum stone color = board_at(b, group_base(group));
 211         assert(color != S_OFFBOARD && color != S_NONE);
 212
 213         if (DEBUGL(5))
 214                 fprintf(stderr, "[%s] 2lib check of color %d\n",
 215                         coord2sstr(group, b), color);
 216
 217         /* Do not try to atari groups that cannot be harmed. */
 218         if (use_miaisafe && miai_2lib(b, group, color))
 219                 return;
 220
 221         can_atari_group(b, group, color, to_play, q, tag, use_def_no_hopeless);
 222
 223         /* Can we counter-atari another group, if we are the defender? */
 224         if (to_play != color)
 225                 return;
 226         foreach_in_group(b, group) {
 227                 foreach_neighbor(b, c, {
 228                         if (board_at(b, c) != stone_other(color))
 229                                 continue;
 230                         group_t g2 = group_at(b, c);
 231                         if (board_group_info(b, g2).libs == 1) {
 232                                 /* We can capture a neighbor. */
 233                                 mq_add(q, board_group_info(b, g2).lib[0], tag);
 234                                 mq_nodup(q);
 235                                 continue;
 236                         }
 237                         if (board_group_info(b, g2).libs != 2)
 238                                 continue;
 239                         can_atari_group(b, g2, stone_other(color), to_play, q, tag, use_def_no_hopeless);
 240                 });
 241         } foreach_in_group_end;
 242 }