HDU 1016 - Prime Ring Problem [简单DFS]

#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstring>
#include <cstdlib>

const int maxn = 1024;
bool checked[maxn] = { 1, 1 };
int pri[maxn], tot = 0;
int n, res[22], kase = 0, vis[22];

void init(){
for (int i = 2; i < maxn; ++i){
if (!checked[i]) pri[tot++] = i;
for (int j = 0; j < tot && pri[j] * i < maxn; ++j){
checked[pri[j] * i] = 1;
if (!(i % pri[j])) break;
}
}
}

void DFS(const int d){
if (d == n){
if (!checked[1 + res[d - 1]]){
for (int i = 0; i < n; ++i)
printf("%d%c", res[i], i == n - 1 ? '\n' : ' ');
}
return;
}
for (int i = 2; i <= n; ++i){
if (!vis[i] && !checked[i + res[d - 1]]){
vis[i] = 1;
res[d] = i; DFS(d + 1);
vis[i] = 0;
}
}
}

int main(){
init();
while (~scanf("%d", &n)) {
printf("Case %d:\n", ++kase);
memset(vis, 0, sizeof(vis));
res[0] = 1; vis[1] = 1;
DFS(1);
printf("\n");
}
return 0;
}