leetcode-563-Binary-Tree-Tilt

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描述

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:

  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.

分析

后序遍历二叉树，可以套模板了。

解决方案1(Javascript)

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/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
let tilt;
var findTilt = function(root) {
    tilt = 0;
    postOrder(root);
    return tilt;
};

var postOrder = function(root) {
    if (root == undefined) {
        return 0;
    }
    let l = postOrder(root.left);
    let r = postOrder(root.right);
    tilt += Math.abs(r-l);
    return root.val + l + r;
}

题目来源