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, int tag)
  62 {
  63         for (int i = 0; i < 2; i++) {
  64                 coord_t lib = board_group_info(b, group).lib[i];
  65                 assert(board_at(b, lib) == S_NONE);
  66                 if (!board_is_valid_play(b, to_play, lib))
  67                         continue;
  68
  69                 /* Don't play at the spot if it is extremely short
  70                  * of liberties... */
  71                 /* XXX: This looks harmful, could significantly
  72                  * prefer atari to throwin:
  73                  *
  74                  * XXXOOOOOXX
  75                  * .OO.....OX
  76                  * XXXOOOOOOX */
  77 #if 0
  78                 if (neighbor_count_at(b, lib, stone_other(owner)) + immediate_liberty_count(b, lib) < 2)
  79                         continue;
  80 #endif
  81
  82                 /* If the move is too "lumpy", do not play it:
  83                  *
  84                  * #######
  85                  * ..O.X.X <- always play the left one!
  86                  * OXXXXXX */
  87                 if (neighbor_count_at(b, lib, stone_other(owner)) + neighbor_count_at(b, lib, S_OFFBOARD) >= 3)
  88                         continue;
  89
  90                 /* If we are the defender not connecting out, do not
  91                  * escape with moves that do not gain liberties anyway
  92                  * - either the new extension has just single extra
  93                  * liberty, or the "gained" liberties are shared. */
  94                 /* XXX: We do not check connecting to a short-on-liberty
  95                  * group (e.g. ourselves). */
  96                 if (to_play == owner && neighbor_count_at(b, lib, owner) == 1) {
  97                         if (immediate_liberty_count(b, lib) == 1)
  98                                 continue;
  99                         if (immediate_liberty_count(b, lib) == 2
 100                             && coord_is_adjecent(lib, board_group_info(b, group).lib[1 - i], b))
 101                                 continue;
 102                 }
 103
 104 #ifdef NO_DOOMED_GROUPS
 105                 /* If the owner can't play at the spot, we don't want
 106                  * to bother either. */
 107                 if (is_bad_selfatari(b, owner, lib))
 108                         continue;
 109 #endif
 110
 111                 /* Of course we don't want to play bad selfatari
 112                  * ourselves, if we are the attacker... */
 113                 if (
 114 #ifdef NO_DOOMED_GROUPS
 115                     to_play != owner &&
 116 #endif
 117                     is_bad_selfatari(b, to_play, lib))
 118                         continue;
 119
 120                 /* Tasty! Crispy! Good! */
 121                 mq_add(q, lib, tag);
 122                 mq_nodup(q);
 123         }
 124 }
 125
 126 void
 127 group_2lib_check(struct board *b, group_t group, enum stone to_play, struct move_queue *q, int tag)
 128 {
 129         enum stone color = board_at(b, group_base(group));
 130         assert(color != S_OFFBOARD && color != S_NONE);
 131
 132         if (DEBUGL(5))
 133                 fprintf(stderr, "[%s] 2lib check of color %d\n",
 134                         coord2sstr(group, b), color);
 135
 136         /* Do not try to atari groups that cannot be harmed. */
 137         if (miai_2lib(b, group, color))
 138                 return;
 139
 140         check_group_atari(b, group, color, to_play, q, tag);
 141
 142         /* Can we counter-atari another group, if we are the defender? */
 143         if (to_play != color)
 144                 return;
 145         foreach_in_group(b, group) {
 146                 foreach_neighbor(b, c, {
 147                         if (board_at(b, c) != stone_other(color))
 148                                 continue;
 149                         group_t g2 = group_at(b, c);
 150                         if (board_group_info(b, g2).libs == 1) {
 151                                 /* We can capture a neighbor. */
 152                                 mq_add(q, board_group_info(b, g2).lib[0], tag);
 153                                 mq_nodup(q);
 154                                 continue;
 155                         }
 156                         if (board_group_info(b, g2).libs != 2)
 157                                 continue;
 158                         check_group_atari(b, g2, color, to_play, q, tag);
 159                 });
 160         } foreach_in_group_end;
 161 }