题目

• 输入一棵二叉树，判断该二叉树是否是平衡二叉树。

思路

• 计算每个左右子树的深度，如果深度之差大于1，那么此二叉树就不是平衡二叉树，否则就是平衡二叉树

代码

• 第一次提交，将计算每个左右子树的深度方法写错了，

import java.util.Queue;
import java.util.LinkedList;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }
}**/
public class Solution {
    public boolean IsBalanced_Solution(TreeNode root) {
         if(root ==null)
                return true;
        boolean flag = IsBalanced_Solution_1(root);
        boolean flag1 = IsBalanced_Solution_1(root.right);
        boolean flag2 = IsBalanced_Solution_1(root.left);
        if(flag==true && flag1==true && flag2==true)
            return true;
        else
            return false;
    }
    public boolean IsBalanced_Solution_1(TreeNode root) {
           if(root ==null)
                return true;
            Queue<TreeNode> queue = new LinkedList<>();
            int lengthleft = 0;
            int lengthright =0;
            if(root==null)
                return true;
            queue.add(root);
            while(queue.size()!=0){
                for(int i=0;i<queue.size();i++){
                    TreeNode temp = queue.poll();
                    if(temp.right!=null){
                        queue.add(temp.right);
                        lengthright++;
                    }
                    if(temp.left!=null){
                        queue.add(temp.left);
                        lengthleft++;
                    }
                }
            }
            int len =0;
            if(lengthright>lengthleft)
                len = lengthright-lengthleft;
            else
                len = lengthleft-lengthright;
            if(len<=1)
                return true;
            else 
                return false;
     }
}

通过的代码

import java.util.Queue;
import java.util.LinkedList;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }
}**/
public class Solution {
    public boolean IsBalanced_Solution(TreeNode root) {
         if(root ==null)
                return true;
        int flag1 = TreeDepth(root.right);
        int flag2 = TreeDepth(root.left);
        int len =0;
        if(flag1>flag2)
            len =flag1-flag2;
        else
            len =flag2-flag1;
        if(len<=1)
            return true;
        else
            return false;
    }
   public int TreeDepth(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<>();
        int length = 0;
        if(root==null)
            return 0;
        queue.add(root);
        while(queue.size()!=0){
            length++;
            for(int i=0;i<queue.size();i++){
                TreeNode temp = queue.poll();
                if(temp.right!=null)
                    queue.add(temp.right);
                if(temp.left!=null)
                    queue.add(temp.left);
            }
        }
        return length;
    }
}

牛客优秀代码

链接：https://www.nowcoder.com/questionTerminal/8b3b95850edb4115918ecebdf1b4d222
来源：牛客网

public class Solution {
    //判断根节点左右子树的深度，高度差超过1，则不平衡
    public boolean IsBalanced_Solution(TreeNode root) {
        if (root==null) {
            return true;
        }
        int left = getTreeDepth(root.left);
        int right = getTreeDepth(root.right);
        return Math.abs(left-right)>1?false:true;
    }
    //求取节点的深度
    public static int getTreeDepth(TreeNode root) {
        if (root==null) {
            return 0;
        }
        int leftDepth = 1+getTreeDepth(root.left);
        int rightDepth = 1+getTreeDepth(root.right);
        return leftDepth>rightDepth?leftDepth:rightDepth;
    }
}