杭电acm解题报告2001---2099.

				#include 
				#include 
				#include 
				#include 
				using namespace std;
				
				int t,n,sum,edge_len;
				int len[30];
				bool flag;
				
				void dfs(int now, int edge,int pos)
				{
					int i,j,t;
				
					if (edge == 3) {
						flag = true;
						return ;
					}
					for (i=pos;i						if (len[i] > 0) {
							t = len[i];
							len[i] = -1;
							j = now + t;
							if (j == edge_len) {
								dfs(0,edge+1,0);
							}
							else if (j < edge_len) {//注意下次起始i+1，前面i+1无法构造出解
								dfs(j, edge, i+1);
							}
							len[i] = t;
							if (flag || edge_len < j) {
								return ;
							}
						}
					}
				}
				
				int main()
				{
					int i,j;
				
					scanf("%d",&t);
					while (t --) {
						scanf("%d",&n);
						sum = 0;
						for (i=0;i							scanf("%d",&len[i]);
							sum += len[i];
						}
						sort(len,len+n);
						flag = false;
						if (sum % 4 == 0) {
							edge_len = sum / 4;
							if (edge_len >= len[n-1]) {
								dfs(0,0,0);
							}
						}
						printf("%s\n", flag ? "yes" : "no");
					}
				}