LeetCode 110 Balanced Binary Tree

题目

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Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

判断是否为平衡二叉树

思路

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1 这道题目的平衡二叉树的定义是： 任何一个节点的左右子树深度 相差不大于1.

2 按照定义，用递归，一个个节点检查。

public class Solution {    public boolean isBalanced(TreeNode root) {        if(root==null){            return true;        }        int left = getheight(root.left);        int right = getheight(root.right);        return (Math.abs(left-right)<=1) && isBalanced(root.left) && isBalanced(root.right) ;    }        public int getheight(TreeNode root){        if(root==null){            return 0;        }        return Math.max(getheight(root.left),getheight(root.right))+1;    }}

3 但是还有一种平衡二叉树定义：相对于root节点，任何叶子节点的深度差距不大于1。

4 这时候只要计算深度最大值和最小值的差值即可。

public static int maxDepth(TreeNode root) {2 if (root == null) {3 return 0;4 }5 return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));6 }78 public static int minDepth(TreeNode root) {9 if (root == null) {10 return 0;11 }12 return 1 + Math.min(minDepth(root.left), minDepth(root.right));13 }1415 public static boolean isBalanced(TreeNode root){16 return (maxDepth(root) - minDepth(root) <= 1);17 }