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[fix] Add heuristic evaluation, fork detection, and Phase 1 win/block split to AI.

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Minimax leaf nodes now return a positional score instead of 0, using
playable-threat detection (±100), non-playable threats (±40), fork
bonus (±200), two-in-a-row (±5), and center control (±3). Phase 1
is split into two passes so the AI never blocks when it can win.
Game sequence is now auto-logged to the browser console on game end.
Applied to all three implementations (C++, JS, Python).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Seppe De Loore
2026-03-27 16:59:55 +01:00
parent 54bae2faf5
commit b27032762e
3 changed files with 64 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files
connect_four.js
+22 -5
View File
@@ -1,6 +1,6 @@
/* ============================================================
* Connect Four — Browser Edition
* A single-file game: AI (minimax + alpha-beta), demo mode,
* A single-file game: AI (minimax + alpha-beta + heuristic), demo mode,
* game log (localStorage), blunder mode, idle timeout.
*
* Include this script in an HTML page that has:
@@ -168,6 +168,7 @@ function scanBoard(b) {
function evaluateBoard(b, aiP, huP) {
let score = 0;
let aiThreats = 0, huThreats = 0;
// Center column bonus
for (let r = 0; r < ROWS; r++) {
@@ -177,16 +178,27 @@ function evaluateBoard(b, aiP, huP) {
// Score a window of 4 cells by piece counts
function scoreWindow(c, r, dc, dr) {
let ai = 0, hu = 0;
let ai = 0, hu = 0, emptyC = -1, emptyR = -1;
for (let i = 0; i < 4; i++) {
const v = b[c + i * dc][r + i * dr];
const cc = c + i * dc;
const rr = r + i * dr;
const v = b[cc][rr];
if (v === aiP) ai++;
else if (v === huP) hu++;
else { emptyC = cc; emptyR = rr; }
}
if (ai > 0 && hu > 0) return 0;
if (ai === 3) return 50;
if (ai === 3) {
aiThreats++;
const playable = emptyR === 0 || b[emptyC][emptyR - 1] !== 0;
return playable ? 100 : 40;
}
if (ai === 2) return 5;
if (hu === 3) return -50;
if (hu === 3) {
huThreats++;
const playable = emptyR === 0 || b[emptyC][emptyR - 1] !== 0;
return playable ? -100 : -40;
}
if (hu === 2) return -5;
return 0;
}
@@ -208,6 +220,10 @@ function evaluateBoard(b, aiP, huP) {
for (let c = 0; c <= COLS - 4; c++)
score += scoreWindow(c, r, 1, -1);
// Fork bonus: multiple threats are disproportionately dangerous
if (aiThreats >= 2) score += 200;
if (huThreats >= 2) score -= 200;
return score;
}
@@ -324,6 +340,7 @@ function checkGameEnd() {
if (gameState !== State.DEMO) {
games = logGame(games, gameMenuMode, gameLevel, won ? w : 0, currentMoves);
console.log(`Game: ${currentMoves} → ${won ? playerName(w) + " wins" : "Draw"}`);
}
gameState = won ? State.FINISHED_WIN : State.FINISHED_DRAW;
demoResetTimer = performance.now() / 1000;
connect_four.py
+22 -5
View File
@@ -1,4 +1,4 @@
"""Connect Four terminal game with AI, using Rich for display."""
"""Connect Four terminal game with AI (minimax + alpha-beta + heuristic), using Rich for display."""
import os
import queue
@@ -271,6 +271,8 @@ def log_game(games: list[dict], game_menu_mode: int, level: int, winner: int, mo
def evaluate_board(board: list[list[int]], ai_p: int, hu_p: int) -> int:
score = 0
ai_threats = 0
hu_threats = 0
# Center column bonus
for r in range(ROWS):
@@ -281,21 +283,30 @@ def evaluate_board(board: list[list[int]], ai_p: int, hu_p: int) -> int:
# Score a window of 4 cells by piece counts
def score_window(c: int, r: int, dc: int, dr: int) -> int:
ai, hu = 0, 0
nonlocal ai_threats, hu_threats
ai, hu, empty_c, empty_r = 0, 0, -1, -1
for i in range(4):
v = board[c + i * dc][r + i * dr]
cc = c + i * dc
rr = r + i * dr
v = board[cc][rr]
if v == ai_p:
ai += 1
elif v == hu_p:
hu += 1
else:
empty_c, empty_r = cc, rr
if ai > 0 and hu > 0:
return 0
if ai == 3:
return 50
ai_threats += 1
playable = empty_r == 0 or board[empty_c][empty_r - 1] != 0
return 100 if playable else 40
if ai == 2:
return 5
if hu == 3:
return -50
hu_threats += 1
playable = empty_r == 0 or board[empty_c][empty_r - 1] != 0
return -100 if playable else -40
if hu == 2:
return -5
return 0
@@ -317,6 +328,12 @@ def evaluate_board(board: list[list[int]], ai_p: int, hu_p: int) -> int:
for c in range(COLS - 3):
score += score_window(c, r, 1, -1)
# Fork bonus: multiple threats are disproportionately dangerous
if ai_threats >= 2:
score += 200
if hu_threats >= 2:
score -= 200
return score
src/main.cpp
+20 -4
View File
@@ -268,6 +268,7 @@ int8_t scanBoard() {
int evaluateBoard(int8_t aiP, int8_t huP) {
int score = 0;
int aiThreats = 0, huThreats = 0;
// Center column bonus
for (int r = 0; r < ROWS; r++) {
@@ -277,16 +278,27 @@ int evaluateBoard(int8_t aiP, int8_t huP) {
// Score a window of 4 cells by piece counts
auto scoreWindow = [&](int c, int r, int dc, int dr) -> int {
int ai = 0, hu = 0;
int ai = 0, hu = 0, emptyC = -1, emptyR = -1;
for (int i = 0; i < 4; i++) {
int8_t v = board[c + i * dc][r + i * dr];
int cc = c + i * dc;
int rr = r + i * dr;
int8_t v = board[cc][rr];
if (v == aiP) ai++;
else if (v == huP) hu++;
else { emptyC = cc; emptyR = rr; }
}
if (ai > 0 && hu > 0) return 0;
if (ai == 3) return 50;
if (ai == 3) {
aiThreats++;
bool playable = emptyR == 0 || board[emptyC][emptyR - 1] != 0;
return playable ? 100 : 40;
}
if (ai == 2) return 5;
if (hu == 3) return -50;
if (hu == 3) {
huThreats++;
bool playable = emptyR == 0 || board[emptyC][emptyR - 1] != 0;
return playable ? -100 : -40;
}
if (hu == 2) return -5;
return 0;
};
@@ -296,6 +308,10 @@ int evaluateBoard(int8_t aiP, int8_t huP) {
for (int r = 0; r < 3; r++) for (int c = 0; c < 4; c++) score += scoreWindow(c, r, 1, 1);
for (int r = 3; r < 6; r++) for (int c = 0; c < 4; c++) score += scoreWindow(c, r, 1, -1);
// Fork bonus: multiple threats are disproportionately dangerous
if (aiThreats >= 2) score += 200;
if (huThreats >= 2) score -= 200;
return score;
}