【Leetcode】Balanced Binary Tree

最新推荐文章于 2025-09-10 22:03:14 发布

转载最新推荐文章于 2025-09-10 22:03:14 发布 · 117 阅读

文章标签：

#leetcode #java #TreeNode #Binary Tree

本文介绍了三种使用Java实现的方法来判断一棵二叉树是否为高度平衡二叉树。高度平衡二叉树定义为：对于树中每一个节点，其两个子树的深度之差不超过1。文中提供了详细的代码实现及思路解析。

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.

Java:

1.http://blog.youkuaiyun.com/linhuanmars/article/details/23731355

public boolean isBalanced(TreeNode root)
{
    return helper(root)>=0;
}
private int helper(TreeNode root)
{
    if(root == null)
        return 0;
    int left = helper(root.left);
    int right = helper(root.right);
    if(left<0 || right<0)
        return -1;
    if(Math.abs(left-right)>=2)
        return -1;
    return Math.max(left,right)+1;
}

2. http://blog.youkuaiyun.com/fightforyourdream/article/details/18693131

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
 public boolean isBalanced(TreeNode root) {  
        if(root == null){  
            return true;  
        }  
        // 如果子树高度差大于1，则不平衡  
        if(Math.abs(depth(root.left)-depth(root.right)) > 1){  
            return false;  
        }  
        // 递归检查左子树和右子树的平衡性  
        return isBalanced(root.left) && isBalanced(root.right);  
    }  
  
    // 帮助方法，返回树的高度  
    private int depth(TreeNode root){  
        if(root == null){  
            return 0;  
        }  
        return 1 + Math.max(depth(root.left), depth(root.right));  
    }  
}

3. http://standalone.iteye.com/blog/1856516

/** 
 * Definition for binary tree 
 * public class TreeNode { 
 *     int val; 
 *     TreeNode left; 
 *     TreeNode right; 
 *     TreeNode(int x) { val = x; } 
 * } 
 */  
public class Solution {  
    public boolean isBalanced(TreeNode root) {  
        return height(root) != -1;  
    }  
  
    private int height(TreeNode root)  
    {  
        if(root == null)  
            return 0;  
  
        int leftHeight = height(root.left);  
        if(leftHeight == -1)  
            return -1;  
  
        int rightHeight = height(root.right);  
        if(rightHeight == -1)  
            return -1;  
  
        if(Math.abs(leftHeight - rightHeight) > 1)  
            return -1;  
  
        return 1 + Math.max(leftHeight, rightHeight);  
    }  
}