题目：

题解：

struct hashTable {int key;UT_hash_handle hh;
};struct hashTable* find(struct hashTable** hashtable, int ikey) {struct hashTable* tmp = NULL;HASH_FIND_INT(*hashtable, &ikey, tmp);return tmp;
}void insert(struct hashTable** hashtable, int ikey) {struct hashTable* tmp = NULL;HASH_FIND_INT(*hashtable, &ikey, tmp);if (tmp == NULL) {tmp = malloc(sizeof(struct hashTable));tmp->key = ikey;HASH_ADD_INT(*hashtable, key, tmp);}
}void erase(struct hashTable** hashtable, int ikey) {struct hashTable* tmp = NULL;HASH_FIND_INT(*hashtable, &ikey, tmp);if (tmp != NULL) {HASH_DEL(*hashtable, tmp);free(tmp);}
}struct hashTable *columns, *diagonals1, *diagonals2;int backtrack(int n, int row) {if (row == n) {return 1;} else {int count = 0;for (int i = 0; i < n; i++) {if (find(&columns, i) != NULL) {continue;}int diagonal1 = row - i;if (find(&diagonals1, diagonal1) != NULL) {continue;}int diagonal2 = row + i;if (find(&diagonals2, diagonal2) != NULL) {continue;}insert(&columns, i);insert(&diagonals1, diagonal1);insert(&diagonals2, diagonal2);count += backtrack(n, row + 1);erase(&columns, i);erase(&diagonals1, diagonal1);erase(&diagonals2, diagonal2);}return count;}
}int totalNQueens(int n) {columns = diagonals1 = diagonals2 = NULL;return backtrack(n, 0);
}