hdu1518 bjfuoj1042 zoj1909 poj2362 经典的搜索加剪枝

bjfuoj的测试数据最水，用很简单的方法一下就过了，又调了好长时间，才过掉其它OJ上的这道题目~

/*
 * hdu1518/win.cpp
 * Created on: 2011-11-8
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <queue>
#include <set>
#include <map>
#include <stack>
#include <string>
#include <vector>
#include <deque>
#include <list>
#include <functional>
#include <numeric>
#include <cctype>
using namespace std;
const int MAXN = 25;
int lens[MAXN];
bool visited[MAXN];
int N, ave, cur_tol_len, totallen;

inline bool cmp(const int &a, const int &b) {
    return a > b;
}

bool myfind(int step, int num) {
    if (num > 3) {
        return true;
    }
    if (step >= N) {
        return false;
    }
    if (!visited[step] && (lens[step] + cur_tol_len) <= ave * num) {
        visited[step] = true;
        cur_tol_len += lens[step];
        if(cur_tol_len == ave * num) {
            if(myfind(0, num + 1)) {
                return true;
            }
        }else if (myfind(step + 1, num)) {
            return true;
        }
        visited[step] = false;
        cur_tol_len -= lens[step];
    }
    return myfind(step + 1, num);
}

bool judge() {
    if (N < 4 || totallen % 4 != 0) {
        return false;
    }
    ave = totallen / 4;
    for (int i = 0; i < N; i++) {
        if (lens[i] > ave) {
            return false;
        }
    }
    sort(lens, lens + N, cmp);
    memset(visited, false, sizeof(visited));
    cur_tol_len = 0;
    return myfind(0, 1);
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    int T;
    scanf("%d", &T);
    while (T--) {
        scanf("%d", &N);
        totallen = 0;
        for (int i = 0; i < N; i++) {
            scanf("%d", &lens[i]);
            totallen += lens[i];
        }
        if (judge()) {
            puts("yes");
        } else {
            puts("no");
        }
    }
    return 0;
}