POJ 2362 Square

题意：给n个木棍，问能不能正好拼成一个正方形。

解法：POJ1011的简单版……不需要太多剪枝……随便剪一剪就好了……但是各种写屎来着QAQ

代码：

#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string>
#include<string.h>
#include<math.h>
#include<limits.h>
#include<time.h>
#include<stdlib.h>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<vector>
#include<iomanip>
#define LL long long
#define lson l, m, rt << 1
#define rson m + 1, r, rt << 1 | 1

using namespace std;

int n;
int stick[25];
bool vis[25];
bool dfs(int len, int remlen, int pos, int num)
{
    if(remlen == 0)
    {
        if(num == 3) return true;
        return dfs(len, len, 0, num + 1);
    }
    for(int i = pos; i < n; i++)
    {
        if(i > 0 && !vis[i - 1] && stick[i] == stick[i - 1]) continue;
        if(!vis[i] && remlen >= stick[i])
        {
            vis[i] = true;
            if(dfs(len, remlen - stick[i], i + 1, num)) return true;
            vis[i] = false;
        }
        if(!vis[i] && i == 0) return false;
    }
    return false;
}
bool cmp(int a, int b)
{
    return a > b;
}
int main()
{
    int T;
    scanf("%d", &T);
    while(T--)
    {
        memset(vis, 0, sizeof vis);
        scanf("%d", &n);
        int sum = 0;
        int maxn = 0;
        for(int i = 0; i < n; i++)
        {
            scanf("%d", &stick[i]);
            sum += stick[i];
            maxn = max(maxn, stick[i]);
        }
        sort(stick, stick + n, cmp);
        if(sum % 4 != 0 || maxn > sum / 4 || n < 4)
        {
            puts("no");
            continue;
        }
        if(dfs(sum / 4, sum / 4, 0, 1)) puts("yes");
        else puts("no");
    }
    return 0;
}