leetcode-563. Binary Tree Tilt

563. Binary Tree Tilt

Given a binary tree, return the tilt of the whole tree.

The tilt of a tree node is defined as the absolute difference between the sum of all left subtree node values and the sum of all right subtree node values. Null node has tilt 0.

The tilt of the whole tree is defined as the sum of all nodes' tilt.

Example:

Input: 
         1
       /   \
      2     3
Output: 1
Explanation: 
Tilt of node 2 : 0
Tilt of node 3 : 0
Tilt of node 1 : |2-3| = 1
Tilt of binary tree : 0 + 0 + 1 = 1

Note:

1. The sum of node values in any subtree won't exceed the range of 32-bit integer.
2. All the tilt values won't exceed the range of 32-bit integer.

求Tilt，每个节点的 tilt 定义为所有左右子树的 差的绝对值。 所求为 所有节点的tilt的和

用递归就很好解决，用left，right来保存左右子树的值，返回左右子树加节点的值，用sum计算和即可

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int sum = 0;
    public int findTilt(TreeNode root) {
        traverse(root);
        return sum;
    }
    
    public int traverse(TreeNode root)
    {
        if(root==null )
            return 0;
        int left=traverse(root.left);
        int right=traverse(root.right);
        sum+=Math.abs(left-right);
        return left+right+root.val;
    }
}