110. Balanced Binary Tree

[Tcdian]

110. Balanced Binary Tree

给定一个二叉树，判断它是否是高度平衡的二叉树。

本题中，一棵高度平衡二叉树定义为：

一个二叉树每个节点 的左右两个子树的高度差的绝对值不超过1。

Example 1

Given the following tree [3,9,20,null,null,15,7]

    3
   / \
  9  20
    /  \
   15   7

Return true.

Example 2

Given the following tree [1,2,2,3,3,null,null,4,4]

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4

Return false.

[Tcdian]

Solution

• JavaScript Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isBalanced = function(root) {
    let maxDifference = 0;
    calcDepth(root);
    return maxDifference <= 1;

    function calcDepth(root) {
        if (maxDifference > 1) {
            return maxDifference;
        }
        if (root === null) {
            return 0;
        }
        const leftDepth = calcDepth(root.left);
        const rightDepth = calcDepth(root.right);
        maxDifference = Math.max(maxDifference, Math.abs(leftDepth - rightDepth));
        return Math.max(leftDepth, rightDepth) + 1;
    }
};

• TypeScript Solution

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function isBalanced(root: TreeNode | null): boolean {
    let maxDifference = 0;
    calcDepth(root);
    return maxDifference <= 1;

    function calcDepth(root: TreeNode | null): number {
        if (maxDifference > 1) {
            return maxDifference;
        }
        if (root === null) {
            return 0;
        }
        const leftDepth = calcDepth(root.left);
        const rightDepth = calcDepth(root.right);
        maxDifference = Math.max(maxDifference, Math.abs(leftDepth - rightDepth));
        return Math.max(leftDepth, rightDepth) + 1;
    }
};