queens

/*
 Author: Cao Beijian
 Result: AC Submission_id: 4271005
 Created at: Sun Apr 03 2022 12:35:17 GMT+0800 (China Standard Time)
 Problem_id: 5439   Time: 3 Memory: 1676
*/

#include <stdio.h>
#include <stdlib.h>
int queens[25] = { 0 }, rows = 0, ans = 0;
char check(int k, int p){//row k col p
    int i;
    for(i = 1; i < k; i++){
        if((queens[i] == p) || (abs(queens[i] - p) == abs(k - i))){
            return 0;
        }
    }
    return 1;
}
void dfs(int k){
    if(k > rows){
        ans++; return;
    }
    else{
        int i;
        for(i = 1; i <= rows; i++){
            if(check(k, i)){
                queens[k] = i;
                dfs(k + 1);
            }
            queens[k] = 0;
        }
    }
}
int main(){
    scanf("%d", &rows);
    dfs(1);
    printf("%d\n", ans);
    return 0;
}