代码随想录算法刷题训练营day17

代码随想录算法刷题训练营day17：LeetCode(110)平衡二叉树

LeetCode(110)平衡二叉树
题目

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isBalanced(TreeNode root) {
        //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 
        if(root==null){
            return true;
        }
        //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 
        //设置一个函数求求左右节点的高度差，并在求的过程中，判断左右节点的高度差
        int flagNode=betweenNodeHeight(root);
        if(flagNode==-1){
            return false;
        }else{
            return true;
        }
    }
    public int betweenNodeHeight(TreeNode root){
        if(root==null){
            return 0;
        }
        //后续遍历，先左子树，再右子树，再根-----一层一层往上返回-1；
        int leftHeight=betweenNodeHeight(root.left);
        if(leftHeight==-1){
            return -1;
        }
        int rightHeight=betweenNodeHeight(root.right);
        if(rightHeight==-1){
            return -1;
        }
        if(Math.abs(leftHeight-rightHeight)>1){
            return -1;
        }else{
            int rootHeight=Math.max(leftHeight, rightHeight)+1;
            return rootHeight;
        }
       
    }
}