563. Binary Tree Tilt

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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:

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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:

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

解法1：

对每一个node计算一个total sum,同时也计算出当前node的sum，然后再把这个sum加入到结果中就可以了。
C++

1

Java

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int totalTilt = 0;
    public int findTilt(TreeNode root) {
        int temp = helper(root);
        return totalTilt;
    }
    private int helper(TreeNode root) {
        if (root == null) {
            return 0;
        }
        if (root.left == null && root.right == null) {
            return root.val;
        }
        int left = helper(root.left);
        int right = helper(root.right);
        totalTilt += Math.abs(left - right);    // update the total tilt
        return left + right + root.val; // return total sum
    }
}