POJ.1145 Tree Summing

1.Problem
http://poj.org/problem?id=1145

2.Idea
Tree pre-order traversing

3.Source

 int tree_sum(int n)  
 {  
      int ans = 0, m;  
      if (scanf(" (%d", &m)) {  
           ans = tree_sum(n - m) + tree_sum(n - m);  
           if (ans < 2) ans = 0;  
      }  
      else  
           ans = !n;  
      scanf(" )");  
      return ans;  
 }  
 int main()  
 {  
      int n;  
      while (scanf("%d", &n) != EOF) {  
           if (tree_sum(n)) printf("yes\n");  
           else printf("no\n");  
      }  
      return 0;  
 }