题目：

题解：

int solutionsSize;char** generateBoard(int* queens, int n) {char** board = (char**)malloc(sizeof(char*) * n);for (int i = 0; i < n; i++) {board[i] = (char*)malloc(sizeof(char) * (n + 1));for (int j = 0; j < n; j++) board[i][j] = '.';board[i][queens[i]] = 'Q', board[i][n] = 0;}return board;
}void backtrack(char*** solutions, int* queens, int n, int row, int* columns, int* diagonals1, int* diagonals2) {if (row == n) {char** board = generateBoard(queens, n);solutions[solutionsSize++] = board;} else {for (int i = 0; i < n; i++) {if (columns[i]) {continue;}int diagonal1 = row - i + n - 1;if (diagonals1[diagonal1]) {continue;}int diagonal2 = row + i;if (diagonals2[diagonal2]) {continue;}queens[row] = i;columns[i] = true;diagonals1[diagonal1] = true;diagonals2[diagonal2] = true;backtrack(solutions, queens, n, row + 1, columns, diagonals1, diagonals2);queens[row] = -1;columns[i] = false;diagonals1[diagonal1] = false;diagonals2[diagonal2] = false;}}
}char*** solveNQueens(int n, int* returnSize, int** returnColumnSizes) {char*** solutions = malloc(sizeof(char**) * 501);solutionsSize = 0;int queens[n];int columns[n];int diagonals1[n + n];int diagonals2[n + n];memset(queens, -1, sizeof(queens));memset(columns, 0, sizeof(columns));memset(diagonals1, 0, sizeof(diagonals1));memset(diagonals2, 0, sizeof(diagonals2));backtrack(solutions, queens, n, 0, columns, diagonals1, diagonals2);*returnSize = solutionsSize;*returnColumnSizes = malloc(sizeof(int*) * solutionsSize);for (int i = 0; i < solutionsSize; i++) {(*returnColumnSizes)[i] = n;}return solutions;
}