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 can_atari_group(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         bool have[2] = { false, false };
  65         bool preference[2] = { true, true };
  66         for (int i = 0; i < 2; i++) {
  67                 coord_t lib = board_group_info(b, group).lib[i];
  68                 assert(board_at(b, lib) == S_NONE);
  69                 if (!board_is_valid_play(b, to_play, lib))
  70                         continue;
  71
  72                 if (DEBUGL(6))
  73                         fprintf(stderr, "checking liberty %s of %s %s, filled by %s\n",
  74                                 coord2sstr(lib, b),
  75                                 stone2str(owner), coord2sstr(group, b),
  76                                 stone2str(to_play));
  77
  78                 /* Don't play at the spot if it is extremely short
  79                  * of liberties... */
  80                 /* XXX: This looks harmful, could significantly
  81                  * prefer atari to throwin:
  82                  *
  83                  * XXXOOOOOXX
  84                  * .OO.....OX
  85                  * XXXOOOOOOX */
  86 #if 0
  87                 if (neighbor_count_at(b, lib, stone_other(owner)) + immediate_liberty_count(b, lib) < 2)
  88                         continue;
  89 #endif
  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                 /* By now, we must be decided we add the move to the
 122                  * queue! */
 123                 have[i] = true;
 124
 125                 /* If the move is too "lumpy", prefer the alternative:
 126                  *
 127                  * #######
 128                  * ..O.X.X <- always play the left one!
 129                  * OXXXXXX */
 130                 /* XXX: Isn't this superseded by the 3-liberty group
 131                  * selfatari check now? */
 132                 if (neighbor_count_at(b, lib, owner) + neighbor_count_at(b, lib, S_OFFBOARD) >= 3)
 133                         preference[i] = false;
 134
 135                 if (DEBUGL(6))
 136                         fprintf(stderr, "liberty %s ready with preference %d\n", coord2sstr(lib, b), preference[i]);
 137
 138                 /* If we prefer only one of the moves, pick that one. */
 139                 if (i == 1 && have[0] && preference[0] != preference[1]) {
 140                         if (!preference[0]) {
 141                                 if (q->move[q->moves - 1] == board_group_info(b, group).lib[0])
 142                                         q->moves--;
 143                                 /* ...else{ may happen, since we call
 144                                  * mq_nodup() and the move might have
 145                                  * been there earlier. */
 146                         } else {
 147                                 assert(!preference[1]);
 148                                 continue;
 149                         }
 150                 }
 151
 152                 /* Tasty! Crispy! Good! */
 153                 mq_add(q, lib, tag);
 154                 mq_nodup(q);
 155         }
 156 }
 157
 158 void
 159 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)
 160 {
 161         enum stone color = board_at(b, group_base(group));
 162         assert(color != S_OFFBOARD && color != S_NONE);
 163
 164         if (DEBUGL(5))
 165                 fprintf(stderr, "[%s] 2lib check of color %d\n",
 166                         coord2sstr(group, b), color);
 167
 168         /* Do not try to atari groups that cannot be harmed. */
 169         if (use_miaisafe && miai_2lib(b, group, color))
 170                 return;
 171
 172         can_atari_group(b, group, color, to_play, q, tag, use_def_no_hopeless);
 173
 174         /* Can we counter-atari another group, if we are the defender? */
 175         if (to_play != color)
 176                 return;
 177         foreach_in_group(b, group) {
 178                 foreach_neighbor(b, c, {
 179                         if (board_at(b, c) != stone_other(color))
 180                                 continue;
 181                         group_t g2 = group_at(b, c);
 182                         if (board_group_info(b, g2).libs == 1) {
 183                                 /* We can capture a neighbor. */
 184                                 mq_add(q, board_group_info(b, g2).lib[0], tag);
 185                                 mq_nodup(q);
 186                                 continue;
 187                         }
 188                         if (board_group_info(b, g2).libs != 2)
 189                                 continue;
 190                         can_atari_group(b, g2, stone_other(color), to_play, q, tag, use_def_no_hopeless);
 191                 });
 192         } foreach_in_group_end;
 193 }