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110.平衡二叉树.js
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110.平衡二叉树.js
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/*
* @lc app=leetcode.cn id=110 lang=javascript
*
* [110] 平衡二叉树
*/
// @lc code=start
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
class TreeInfo {
constructor(height, balanced) {
this.height = height;
this.balanced = balanced;
}
}
/**
* @param {TreeNode} root
* @return {boolean}
*/
var isBalanced = function (root) {
// Return whether or not the tree at root is balanced while also storing
// the tree's height in a reference variable.
let isBalancedTreeHelper = function (root) {
// An empty tree is balanced and has height = -1
if (root == null) {
return new TreeInfo(-1, true);
}
// Check subtrees to see if they are balanced.
let left = isBalancedTreeHelper(root.left);
if (!left.balanced) {
return new TreeInfo(-1, false);
}
let right = isBalancedTreeHelper(root.right);
if (!right.balanced) {
return new TreeInfo(-1, false);
}
// Use the height obtained from the recursive calls to
// determine if the current node is also balanced.
if (Math.abs(left.height - right.height) < 2) {
return new TreeInfo(Math.max(left.height, right.height) + 1, true);
}
return new TreeInfo(-1, false);
}
return isBalancedTreeHelper(root).balanced;
};
// @lc code=end