ACM学习历程—HDU1716 排列2（dfs && set容器）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <set>
#define LL long long

using namespace std;

int a[5];
bool vis[5];
set <int> ans;

void dfs(int now, int val)
{
    if (now == 4)
    {
        if (val >= 1000)
            ans.insert(val);
        return;
    }
    for (int i = 0; i < 4; ++i)
    {
        if (vis[i])
            continue;
        vis[i] = true;
        dfs(now+1, val*10+a[i]);
        vis[i] = false;
    }
}

void Work()
{
    ans.clear();
    memset(vis, 0, sizeof(vis));
    dfs(0, 0);
    set <int>::iterator it;
    int high = -1;
    bool flag = false;
    for (it = ans.begin(); it != ans.end(); ++it)
    {
        if (high == -1)
            high = *it/1000;
        if (high != -1 && *it/1000 != high)
        {
            printf("\n");
            high = *it/1000;
            flag = false;
        }
        if (flag)
            printf(" ");
        printf("%d", *it);
        flag = true;
    }
    printf("\n");
}

int main()
{
    //freopen("test.in", "r", stdin);
    bool flag = false;
    while (scanf("%d%d%d%d", &a[0], &a[1], &a[2], &a[3]) != EOF &&
           (a[0]+a[1]+a[2]+a[3]))
    {
        if (flag)
            printf("\n");
        Work();
        flag = true;
    }
    return 0;
}