poj_2362

Square

Time Limit: 3000MS Memory Limit: 65536KTotal Submissions: 19036 Accepted: 6600

Description

Given a set of sticks of various lengths, is it possible to join them end-to-end to form a square?

Input

The first line of input contains N, the number of test cases. Each test case begins with an integer 4 <= M <= 20, the number of sticks. M integers follow; each gives the length of a stick - an integer between 1 and 10,000.

Output

For each case, output a line containing "yes" if is is possible to form a square; otherwise output "no".

Sample Input

34 1 1 1 15 10 20 30 40 508 1 7 2 6 4 4 3 5

Sample Output

yesnoyes

#include <stdio.h>#include <string.h>int arr[21];int m, bian;int he;int visit[21];int f;void dfs(int st, int len, int sum){    if (sum >= 3)    {        f = 1;        return ;    }    if (f)        return ;    if (len > bian)        return ;    if (len == bian)    {        dfs(0, 0, sum + 1);    }    int i;    for (i = st; i < m; i++)    {        if (!visit[i])        {            visit[i] = 1;            dfs(i + 1, len + arr[i], sum);            visit[i] = 0;        }    }}int main(){    int n;    scanf("%d", &n);    while (n--)    {        memset(visit, 0, sizeof(visit));        he = f = 0;        int i;        scanf("%d", &m);        int sum = 0;        for (i = 0; i < m; i++)        {            scanf("%d", &arr[i]);            sum += arr[i];        }        if (sum % 4 != 0)        {            printf("no\n");            continue;        }        bian = sum / 4;        dfs(0, 0, 0);        if (f)        {            printf("yes\n");        }        else            printf("no\n");    }    return 0;}