#include <stdio.h>
#define N 4
int board[N][N];
int isSafe(int row, int col) {
for (int i = 0; i < row; i++) {
if (board[i][col])
return 0;
}
for (int i = row, j = col; i >= 0 && j >= 0; i--, j--) {
if (board[i][j])
return 0;
}
for (int i = row, j = col; i >= 0 && j < N; i--, j++) {
if (board[i][j])
return 0;
}
return 1;
}
int solveNQueens(int row) {
if (row == N) {
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
printf("%s ", board[i][j] ? "O" : "X");
}
printf("\n");
}
printf("\n");
return 1;
}
int count = 0;
for (int col = 0; col < N; col++) {
if (isSafe(row, col)) {
board[row][col] = 1;
count += solveNQueens(row + 1);
board[row][col] = 0;
}
}
return count;
}
int main() {
int count = solveNQueens(0);
printf("共有 %d 种解决方案。\n", count);
return 0;
}