#include<bits/stdc++.h>
using namespace std;
int n = 3;
bool hashtable[100] = {false};
int P[100] = {-1};
int count_num = 0;
void f(int index){if(index == n + 1){for (int i = 1; i <= n; i++){printf("%d ", P[i]);}count_num++;printf("\n");return;}for (int x = 1; x <= n; x++){if (hashtable[x] == false){P[index] = x;hashtable[x] = true;f(index + 1);hashtable[x] = false;}}
}int main(){f(1);printf("\ncount=%d", count_num);return 0;
}

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 int n = 4;
 4 int P[9] = {0};
 5 int cntnum = 0;
 6 bool tablehash[9] = {false};
 7
 8 void f(int index){
 9     if (index == n + 1){
10         bool flag = true;
11         for (int i = 1; i <= n; i++){
12             for (int j = i + 1; j <= n; j++){
13                 if (abs(i - j) == abs(P[i] - P[j])){
14                     flag = false;
15                 }
16             }
17         }
18         if (flag){
19             for (int k= 1; k <= n; k++){
20                 printf("%d ", P[k]);
21             }
22             printf("\n");
23             cntnum++;
24         }
25         return;
26     }
27     for (int i = 1; i <= n; i++){
28         if (tablehash[i] == false){
29             P[index] = i;
30             tablehash[i] = true;
31             f(index + 1);
32             tablehash[i] = false;
33         }
34     }
35 }
36 int main(){
37     f(1);
38     printf("%d", cntnum);
39     return 0;
40 }

#include<bits/stdc++.h>
using namespace std;
int n = 9;
int P[30] = {0};
int cntnum = 0;
bool tablehash[30] = {false};void f(int index){if (index == n + 1){cntnum++;for (int k = 1; k <= n; k++){printf("%d ", P[k]);}printf("\n");return;}for (int i = 1; i <= n; i++){bool flag = true;if (tablehash[i] == false){//假如第i行没有皇后, 即放在第 i 行第 index 列for (int j = 1; j < index; j++){//遍历和以前的皇后是否合法if (abs(index - j) == abs(P[j] - i)){flag = false;break;}}if (flag){//目前可以在第i行第index列放入皇后P[index] = i;tablehash[i] = true;f(index + 1);tablehash[i] = false;}}}}int main(){f(1);//printf("%d", cntnum);printf("%d", cntnum);return 0;
}