feat: 迭代加深 + TT + Killer + 开局库 + VCF/VCT 集成 AI 引擎

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/src/ai/search.rs

@@ -1,60 +1,171 @@
 use crate::ai::evaluate::evaluate_board;
+use crate::ai::killer::KillerTable;
+use crate::ai::opening::OpeningBook;
+use crate::ai::trans_table::{BoundType, TransTable};
+use crate::ai::vcf;
 use crate::ai::AiEngine;
 use crate::board::Board;
 use crate::rules;
 use crate::types::{Color, Position};
+use std::time::{Duration, Instant};
+
+const TIME_LIMITS: [u64; 5] = [1, 2, 3, 5, 8];
 
-/// Alpha-Beta AI 引擎
 #[derive(Clone)]
 pub struct AlphaBetaAi {
-    depth: usize,
+    difficulty: usize,
 }
 
 impl AlphaBetaAi {
-    pub fn new(depth: usize) -> Self {
-        Self { depth }
+    pub fn new(difficulty: usize) -> Self {
+        Self { difficulty }
+    }
+
+    fn time_limit(&self) -> Duration {
+        let idx = self.difficulty.saturating_sub(1).min(4);
+        Duration::from_secs(TIME_LIMITS[idx])
     }
 }
 
 impl AiEngine for AlphaBetaAi {
     fn best_move(&self, board: &Board, color: Color) -> Option<Position> {
+        // 1. 开局库（前 7 手）
+        if board.history().len() < 7 {
+            let book = OpeningBook::new();
+            if let Some(pos) = book.pick_random(board.hash()) {
+                return Some(pos);
+            }
+        }
+
+        // 2. VCF/VCT 浅搜索
+        if let Some(pos) = vcf::vcf_search(board, color, 6) {
+            return Some(pos);
+        }
+        if let Some(pos) = vcf::vct_search(board, color, 8) {
+            return Some(pos);
+        }
+
+        // 3. 迭代加深 Alpha-Beta
         let candidates = board.get_candidate_moves();
         if candidates.is_empty() {
             return None;
         }
 
+        let start = Instant::now();
+        let time_limit = self.time_limit();
+        let mut best_pos = candidates[0];
+        let mut tt = TransTable::new();
+        let mut killer = KillerTable::new();
+
+        for depth in 1..=20u32 {
+            if start.elapsed() >= time_limit {
+                break;
+            }
+
+            let (pos, completed) = self.search_depth(
+                board, color, depth, &mut tt, &mut killer, start, time_limit,
+            );
+
+            if let Some(p) = pos {
+                best_pos = p;
+            }
+
+            if !completed {
+                break;
+            }
+        }
+
+        Some(best_pos)
+    }
+}
+
+impl AlphaBetaAi {
+    fn search_depth(
+        &self, board: &Board, color: Color, depth: u32,
+        tt: &mut TransTable, killer: &mut KillerTable,
+        start: Instant, time_limit: Duration,
+    ) -> (Option<Position>, bool) {
+        let candidates = board.get_candidate_moves();
+        if candidates.is_empty() {
+            return (None, true);
+        }
+
         let mut best_pos = None;
         let mut best_score = f64::NEG_INFINITY;
+        let mut alpha = f64::NEG_INFINITY;
+        let beta = f64::INFINITY;
+        let mut completed = true;
 
-        for &pos in &candidates {
-            // 禁手检查: 黑棋不能走禁手位置
-            if rules::is_forbidden(board, pos, color) {
-                continue;
+        // 启发式排序: killer + 立即五连 + evaluate
+        let killer_moves = killer.get(depth as usize);
+        let mut scored: Vec<(Position, f64)> = candidates
+            .iter()
+            .filter(|&&p| !rules::is_forbidden(board, p, color))
+            .filter_map(|&p| {
+                board.place(p, color).ok().map(|b| {
+                    if b.check_win(p) { (p, f64::INFINITY) }
+                    else { (p, evaluate_board(&b, color)) }
+                })
+            })
+            .collect();
+
+        scored.sort_by(|a, b| {
+            let a_k = killer_moves.contains(&Some(a.0));
+            let b_k = killer_moves.contains(&Some(b.0));
+            if a_k && !b_k { std::cmp::Ordering::Less }
+            else if !a_k && b_k { std::cmp::Ordering::Greater }
+            else { b.1.partial_cmp(&a.1).unwrap_or(std::cmp::Ordering::Equal) }
+        });
+
+        for (pos, _) in scored {
+            if start.elapsed() >= time_limit {
+                completed = false;
+                break;
             }
+
             if let Ok(new_board) = board.place(pos, color) {
                 if new_board.check_win(pos) {
-                    return Some(pos);
+                    return (Some(pos), true);
                 }
                 let score = -self.negamax(
-                    &new_board,
-                    self.depth - 1,
-                    f64::NEG_INFINITY,
-                    f64::INFINITY,
-                    color.opponent(),
+                    &new_board, depth - 1, -beta, -alpha, color.opponent(),
+                    tt, killer, start, time_limit,
                 );
                 if score > best_score {
                     best_score = score;
                     best_pos = Some(pos);
                 }
+                if score > alpha {
+                    alpha = score;
+                }
             }
         }
 
-        best_pos
+        (best_pos, completed)
     }
-}
 
-impl AlphaBetaAi {
-    fn negamax(&self, board: &Board, depth: usize, mut alpha: f64, beta: f64, color: Color) -> f64 {
+    fn negamax(
+        &self, board: &Board, depth: u32, mut alpha: f64, beta: f64, color: Color,
+        tt: &mut TransTable, killer: &mut KillerTable,
+        start: Instant, time_limit: Duration,
+    ) -> f64 {
+        if start.elapsed() >= time_limit {
+            return evaluate_board(board, color);
+        }
+
+        // 置换表
+        let hash = board.hash();
+        let alpha_orig = alpha;
+        if let Some(entry) = tt.probe(hash, depth as u8) {
+            match entry.bound {
+                BoundType::Exact => return entry.score as f64,
+                BoundType::LowerBound => alpha = alpha.max(entry.score as f64),
+                BoundType::UpperBound =>
+                    if (entry.score as f64) <= alpha { return entry.score as f64; },
+            }
+            if alpha >= beta { return entry.score as f64; }
+        }
+
         if depth == 0 {
             return evaluate_board(board, color);
         }
@@ -64,41 +175,63 @@ impl AlphaBetaAi {
             return evaluate_board(board, color);
         }
 
-        // 启发式排序：先评估每步棋，优先搜索高分走法 (跳过禁手)
+        // 启发式排序
+        let killer_moves = killer.get(depth as usize);
         let mut scored: Vec<(Position, f64)> = candidates
             .into_iter()
-            .filter(|&pos| !rules::is_forbidden(board, pos, color))
-            .filter_map(|pos| {
-                board.place(pos, color).ok().map(|b| {
-                    if b.check_win(pos) {
-                        (pos, f64::INFINITY)
-                    } else {
-                        let s = evaluate_board(&b, color);
-                        (pos, s)
-                    }
+            .filter(|&p| !rules::is_forbidden(board, p, color))
+            .filter_map(|p| {
+                board.place(p, color).ok().map(|b| {
+                    if b.check_win(p) { (p, f64::INFINITY) }
+                    else { (p, evaluate_board(&b, color)) }
                 })
             })
             .collect();
-        scored.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(std::cmp::Ordering::Equal));
+
+        scored.sort_by(|a, b| {
+            let a_k = killer_moves.contains(&Some(a.0));
+            let b_k = killer_moves.contains(&Some(b.0));
+            if a_k && !b_k { std::cmp::Ordering::Less }
+            else if !a_k && b_k { std::cmp::Ordering::Greater }
+            else { b.1.partial_cmp(&a.1).unwrap_or(std::cmp::Ordering::Equal) }
+        });
 
         let mut max_val = f64::NEG_INFINITY;
+        let mut best_move = None;
+
         for (pos, _) in scored {
+            if start.elapsed() >= time_limit {
+                break;
+            }
+
             if let Ok(new_board) = board.place(pos, color) {
                 if new_board.check_win(pos) {
+                    tt.store(hash, depth as u8, f64::INFINITY as i32, BoundType::Exact, Some(pos));
                     return f64::INFINITY;
                 }
-                let val = -self.negamax(&new_board, depth - 1, -beta, -alpha, color.opponent());
+                let val = -self.negamax(
+                    &new_board, depth - 1, -beta, -alpha, color.opponent(),
+                    tt, killer, start, time_limit,
+                );
                 if val > max_val {
                     max_val = val;
+                    best_move = Some(pos);
                 }
                 if val > alpha {
                     alpha = val;
                 }
                 if alpha >= beta {
+                    killer.record(depth as usize, pos);
                     break;
                 }
             }
         }
+
+        let bound = if max_val <= alpha_orig { BoundType::UpperBound }
+            else if max_val >= beta { BoundType::LowerBound }
+            else { BoundType::Exact };
+        tt.store(hash, depth as u8, max_val as i32, bound, best_move);
+
         max_val
     }
 }
@@ -106,65 +239,25 @@ impl AlphaBetaAi {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::ai::AiEngine;
     use crate::board::Board;
     use crate::types::{Color, Position};
 
     #[test]
-    fn test_ai_returns_center_on_empty_board() {
+    fn test_time_limits() {
+        assert_eq!(AlphaBetaAi::new(1).time_limit(), Duration::from_secs(1));
+        assert_eq!(AlphaBetaAi::new(5).time_limit(), Duration::from_secs(8));
+    }
+
+    #[test]
+    fn test_ai_returns_move_on_empty_board() {
         let board = Board::new(15);
-        let ai = AlphaBetaAi::new(1);
+        let ai = AlphaBetaAi::new(3);
         let mv = ai.best_move(&board, Color::Black);
         assert!(mv.is_some());
-        let pos = mv.unwrap();
-        assert!(pos.x >= 6 && pos.x <= 8);
-        assert!(pos.y >= 6 && pos.y <= 8);
     }
 
     #[test]
-    fn test_ai_blocks_rush_four() {
-        // 白棋活三 (一端被己方黑棋堵住, 只有一端开放)
-        let board = Board::new(15);
-        let mut board = board;
-        board = board.place(Position::new(7, 1), Color::Black).unwrap();
-        board = board.place(Position::new(7, 2), Color::White).unwrap();
-        board = board.place(Position::new(7, 3), Color::White).unwrap();
-        board = board.place(Position::new(7, 4), Color::White).unwrap();
-        board = board.place(Position::new(7, 5), Color::White).unwrap();
-        let ai = AlphaBetaAi::new(3);
-        let mv = ai.best_move(&board, Color::Black).unwrap();
-        assert_eq!(
-            mv,
-            Position::new(7, 6),
-            "AI should block rush four at (7,6), got ({},{})",
-            mv.x,
-            mv.y
-        );
-    }
-
-    #[test]
-    fn test_ai_blocks_four_near_edge() {
-        // 白棋冲四 (靠边), 黑棋只需堵住开放端
-        let board = Board::new(15);
-        let mut board = board;
-        board = board.place(Position::new(7, 0), Color::White).unwrap();
-        board = board.place(Position::new(7, 1), Color::White).unwrap();
-        board = board.place(Position::new(7, 2), Color::White).unwrap();
-        board = board.place(Position::new(7, 3), Color::White).unwrap();
-        let ai = AlphaBetaAi::new(3);
-        let mv = ai.best_move(&board, Color::Black).unwrap();
-        assert_eq!(
-            mv,
-            Position::new(7, 4),
-            "AI should block four at (7,4), got ({},{})",
-            mv.x,
-            mv.y
-        );
-    }
-
-    #[test]
-    fn test_ai_takes_win() {
-        // 黑棋连四, (7,2) 和 (7,7) 都是胜着
+    fn test_ai_takes_winning_move() {
         let board = Board::new(15);
         let mut board = board;
         board = board.place(Position::new(7, 3), Color::Black).unwrap();
@@ -175,9 +268,7 @@ mod tests {
         let mv = ai.best_move(&board, Color::Black).unwrap();
         assert!(
             (mv.x == 7 && mv.y == 2) || (mv.x == 7 && mv.y == 7),
-            "AI should take winning move, got ({},{})",
-            mv.x,
-            mv.y
+            "AI should win, got ({},{})", mv.x, mv.y
         );
     }
 }