hdu 1518 Square

Square

Time Limit: 10000/5000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 8250 Accepted Submission(s): 2684


Problem 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

3
4 1 1 1 1
5 10 20 30 40 50
8 1 7 2 6 4 4 3 5

Sample Output

yes
no
yes

Source University of Waterloo Local Contest 2002.09.21

題意：給出n條邊長看是否能組成一個正方形

方法：深搜加剪枝

#include
#include
#include
#include
using namespace std;
int n,a[25],vis[25],sum;
int cmp(int a,int b)
{
    return a>b;
}
int dfs(int l,int x,int ans)
{
    int i;
    if(ans==3)
        return 1;
    for(i=x;isum/4)
                printf("no\n");
            else if(dfs(0,0,0))
                printf("yes\n");
            else
                printf("no\n");
    }
    return 0;
}