DFS POJ 2362 Square

题目传送门

 /*
     DFS：问能否用小棍子组成一个正方形
     剪枝有3：长的不灵活，先考虑；若根本构不成正方形，直接no；若第一根比边长长，no
     这题是POJ_1011的精简版:)
 */
 #include <cstdio>
 #include <iostream>
 #include <cstring>
 #include <map>
 #include <set>
 #include <cmath>
 #include <algorithm>
 using namespace std;

 const int MAXN = ;
 const int INF = 0x3f3f3f3f;
 int a[MAXN];
 bool vis[MAXN];
 int len, sum;
 int n, m;

 bool cmp(int x, int y)
 {
     return x > y;
 }

 bool DFS(int ans, int cnt, int s)
 {
     if (cnt == )
     {
         return true;
     }

     for (int i=s; i<=m; ++i)
     {
         if (!vis[i] && ans + a[i] <= len)
         {
             vis[i] = true;
             if (ans + a[i] == len)
             {
                 if (DFS (, cnt + , ) == true)    return true;
                 vis[i] = false;
             }
             else
             {
                 if (DFS (ans + a[i], cnt, i) == true)  return true;
                 vis[i] = false;
             }
         }
     }

     return false;
 }

 int main(void)      //POJ 2362 Square
 {
     //freopen ("POJ_2362.in", "r", stdin);

     scanf ("%d", &n);
     while (n--)
     {
         sum = ;
         memset (vis, , sizeof (vis));

         scanf ("%d", &m);
         for (int i=; i<=m; ++i)
         {
             scanf ("%d", &a[i]);
             sum += a[i];
         }
         sort (a+, a++m, cmp);     //Cut 1

         if (m <  || sum %  != )      //Cut 2
         {
             puts ("no");    continue;
         }
         len = sum / ;

         if (a[] > len)     //Cut 3
         {
             puts ("no");        continue;
         }

         if (DFS (, , ) == true) puts ("yes");
         else    puts ("no");
     }

     return ;
 }

 /*
 yes
 no
 yes
 */