Count Nodes Equal to Sum of Descendants

给一个二叉树, 问上面有多少个node的val等于左子树和右子树的和.

这题就travseal 一下就行了

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    int res = 0;
    public int equalToDescendants(TreeNode root) {
        count(root);
        return res;
    }
    
    public int count(TreeNode root){
        if(root == null)
            return 0;
        int left = count(root.left);
        int right = count(root.right);
        if(root.val == left+right)
            res++;
        return root.val + left + right;
    }
}