Data commit

Task/Tic-tac-toe/C/tic-tac-toe.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+int b[3][3]; /* board. 0: blank; -1: computer; 1: human */
+
+int check_winner()
+{
+	int i;
+	for (i = 0; i < 3; i++) {
+		if (b[i][0] && b[i][1] == b[i][0] && b[i][2] == b[i][0])
+			return b[i][0];
+		if (b[0][i] && b[1][i] == b[0][i] && b[2][i] == b[0][i])
+			return b[0][i];
+	}
+	if (!b[1][1]) return 0;
+
+	if (b[1][1] == b[0][0] && b[2][2] == b[0][0]) return b[0][0];
+	if (b[1][1] == b[2][0] && b[0][2] == b[1][1]) return b[1][1];
+
+	return 0;
+}
+
+void showboard()
+{
+	const char *t = "X O";
+	int i, j;
+	for (i = 0; i < 3; i++, putchar('\n'))
+		for (j = 0; j < 3; j++)
+			printf("%c ", t[ b[i][j] + 1 ]);
+	printf("-----\n");
+}
+
+#define for_ij for (i = 0; i < 3; i++) for (j = 0; j < 3; j++)
+int best_i, best_j;
+int test_move(int val, int depth)
+{
+	int i, j, score;
+	int best = -1, changed = 0;
+
+	if ((score = check_winner())) return (score == val) ? 1 : -1;
+
+	for_ij {
+		if (b[i][j]) continue;
+
+		changed = b[i][j] = val;
+		score = -test_move(-val, depth + 1);
+		b[i][j] = 0;
+
+		if (score <= best) continue;
+		if (!depth) {
+			best_i = i;
+			best_j = j;
+		}
+		best = score;
+	}
+
+	return changed ? best : 0;
+}
+
+const char* game(int user)
+{
+	int i, j, k, move, win = 0;
+	for_ij b[i][j] = 0;
+
+	printf("Board postions are numbered so:\n1 2 3\n4 5 6\n7 8 9\n");
+	printf("You have O, I have X.\n\n");
+	for (k = 0; k < 9; k++, user = !user) {
+		while(user) {
+			printf("your move: ");
+			if (!scanf("%d", &move)) {
+				scanf("%*s");
+				continue;
+			}
+			if (--move < 0 || move >= 9) continue;
+			if (b[i = move / 3][j = move % 3]) continue;
+
+			b[i][j] = 1;
+			break;
+		}
+		if (!user) {
+			if (!k) { /* randomize if computer opens, less boring */
+				best_i = rand() % 3;
+				best_j = rand() % 3;
+			} else
+				test_move(-1, 0);
+
+			b[best_i][best_j] = -1;
+			printf("My move: %d\n", best_i * 3 + best_j + 1);
+		}
+
+		showboard();
+		if ((win = check_winner()))
+			return win == 1 ? "You win.\n\n": "I win.\n\n";
+	}
+	return "A draw.\n\n";
+}
+
+int main()
+{
+	int first = 0;
+	while (1) printf("%s", game(first = !first));
+	return 0;
+}