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 void
  60 check_group_atari(struct board *b, group_t group, enum stone owner,
  61                   enum stone to_play, struct move_queue *q,
  62                   int tag, bool use_def_no_hopeless)
  63 {
  64         for (int i = 0; i < 2; i++) {
  65                 coord_t lib = board_group_info(b, group).lib[i];
  66                 assert(board_at(b, lib) == S_NONE);
  67                 if (!board_is_valid_play(b, to_play, lib))
  68                         continue;
  69
  70                 /* Don't play at the spot if it is extremely short
  71                  * of liberties... */
  72                 /* XXX: This looks harmful, could significantly
  73                  * prefer atari to throwin:
  74                  *
  75                  * XXXOOOOOXX
  76                  * .OO.....OX
  77                  * XXXOOOOOOX */
  78 #if 0
  79                 if (neighbor_count_at(b, lib, stone_other(owner)) + immediate_liberty_count(b, lib) < 2)
  80                         continue;
  81 #endif
  82
  83                 /* If the move is too "lumpy", do not play it:
  84                  *
  85                  * #######
  86                  * ..O.X.X <- always play the left one!
  87                  * OXXXXXX */
  88                 if (neighbor_count_at(b, lib, stone_other(owner)) + neighbor_count_at(b, lib, S_OFFBOARD) >= 3)
  89                         continue;
  90
  91                 /* If we are the defender not connecting out, do not
  92                  * escape with moves that do not gain liberties anyway
  93                  * - either the new extension has just single extra
  94                  * liberty, or the "gained" liberties are shared. */
  95                 /* XXX: We do not check connecting to a short-on-liberty
  96                  * group (e.g. ourselves). */
  97                 if (use_def_no_hopeless && to_play == owner && neighbor_count_at(b, lib, owner) == 1) {
  98                         if (immediate_liberty_count(b, lib) == 1)
  99                                 continue;
 100                         if (immediate_liberty_count(b, lib) == 2
 101                             && coord_is_adjecent(lib, board_group_info(b, group).lib[1 - i], b))
 102                                 continue;
 103                 }
 104
 105 #ifdef NO_DOOMED_GROUPS
 106                 /* If the owner can't play at the spot, we don't want
 107                  * to bother either. */
 108                 if (is_bad_selfatari(b, owner, lib))
 109                         continue;
 110 #endif
 111
 112                 /* Of course we don't want to play bad selfatari
 113                  * ourselves, if we are the attacker... */
 114                 if (
 115 #ifdef NO_DOOMED_GROUPS
 116                     to_play != owner &&
 117 #endif
 118                     is_bad_selfatari(b, to_play, lib))
 119                         continue;
 120
 121                 /* Tasty! Crispy! Good! */
 122                 mq_add(q, lib, tag);
 123                 mq_nodup(q);
 124         }
 125 }
 126
 127 void
 128 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)
 129 {
 130         enum stone color = board_at(b, group_base(group));
 131         assert(color != S_OFFBOARD && color != S_NONE);
 132
 133         if (DEBUGL(5))
 134                 fprintf(stderr, "[%s] 2lib check of color %d\n",
 135                         coord2sstr(group, b), color);
 136
 137         /* Do not try to atari groups that cannot be harmed. */
 138         if (use_miaisafe && miai_2lib(b, group, color))
 139                 return;
 140
 141         check_group_atari(b, group, color, to_play, q, tag, use_def_no_hopeless);
 142
 143         /* Can we counter-atari another group, if we are the defender? */
 144         if (to_play != color)
 145                 return;
 146         foreach_in_group(b, group) {
 147                 foreach_neighbor(b, c, {
 148                         if (board_at(b, c) != stone_other(color))
 149                                 continue;
 150                         group_t g2 = group_at(b, c);
 151                         if (board_group_info(b, g2).libs == 1) {
 152                                 /* We can capture a neighbor. */
 153                                 mq_add(q, board_group_info(b, g2).lib[0], tag);
 154                                 mq_nodup(q);
 155                                 continue;
 156                         }
 157                         if (board_group_info(b, g2).libs != 2)
 158                                 continue;
 159                         check_group_atari(b, g2, color, to_play, q, tag, use_def_no_hopeless);
 160                 });
 161         } foreach_in_group_end;
 162 }