HDU - 1016 DFS+回溯

版权声明：博主的博客不值钱随便转载但要注明出处 https://blog.csdn.net/easylovecsdn/article/details/82749042

基础dfs加了点回溯的思想，WA了一发原因是输出结果没加冒号，ORZ。

#include <bits/stdc++.h>

using namespace std;

int num[25];
bool vis[25];
bool prime[50];

int n;

void get_prime()
{
    memset(prime, true, sizeof(prime));
    prime[0] = false;
    prime[1] = false;

    for (int i = 2; i < 50; i++) {
        for (int j = 2; i*j < 50; j++) {
            prime[i*j] = false;
        }
    }
}


void dfs(int inx, int times)
{
    num[times] = inx;

    if (times == n-1) {
        int sum = num[times] + num[0];
        if (prime[sum]) {
            for (int i = 0; i < n; i++) {
                if (i) cout << " " ;
                cout << num[i] ;
            }
            cout << endl;
        }
        return ;
    }

    for (int i = 2; i <= n; i++) {
        if (!vis[i] && prime[i+inx]) {
            vis[i] = true;
            dfs(i, times+1);
            vis[i] = false;
        }
    }
}

void Memset()
{
    memset(vis, false, sizeof(vis));
    vis[1] = true;
}

int main()
{
    ios::sync_with_stdio(false);
    int cas = 1;
    num[0] = 1;
    get_prime();

    while (cin >> n)
    {
        Memset();
        cout << "Case " << cas++ << ":" << endl;
        for (int i = 2; i <= n; i++) {

            if (prime[1+i]) {
                vis[i] = true;
                dfs(i, 1);
                vis[i] = false;
            }

        }
        cout << endl;
    }

    return 0;
}