UVa 524 - Prime Ring Problem（回溯）

#include<iostream>
#include<cstdio>
#include<string>
#include<algorithm>
#define MAXN 50
using namespace std;

int n, A[MAXN] = {1}, ispe[MAXN], vis[MAXN];

void dfs(int cur) {
if(cur == n&& ispe[A[0] + A[n - 1]]) {
for(int i = 0; i < n; i++) {
i ? printf(" %d", A[i]) : printf("%d", A[i]);
}
printf("\n");
} else for(int i = 2; i <= n; i++) {
if(!vis[i]&& ispe[i + A[cur - 1]]) {
A[cur] = i;
vis[i] = 1;
dfs(cur + 1);
vis[i] = 0;
}
}
}

int main() {
for(int i = 2; i <= 50; i++)
ispe[i] = 1;
for(int i = 2; i <= 50; i++)
for(int j = i + i; j + i <= 50; j += i)
ispe[j] = 0;
int kase = 0;
while(cin >> n) {
if(kase++)
printf("\n");
printf("Case %d:\n", kase);
dfs(1);
}
return 0;
}