Leetcode: Balanced Binary Tree

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 ofevery node never differ by more than 1.

Top down solution.

/**
* 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) {
// Start typing your Java solution below
// DO NOT write main() function
if(root == null)
return true;
while(root != null){
int left = maxHeight(root.left);
int right = maxHeight(root.right);
if(Math.abs(left - right) > 1)
return false;
else
return isBalanced(root.left) && isBalanced(root.right);
}
return false;
}

public int maxHeight(TreeNode root){
if(root == null)
return 0;
int left = maxHeight(root.left) + 1;
int right = maxHeight(root.right) + 1;
return left > right ? left : right;
}
}

Bottom up solution.

/**
* 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){
// Start typing your Java solution below
// DO NOT write main() function
return decide(root) >= 0 ? true : false;
}
public int decide(TreeNode root){
if(root == null)
return 0;
int left = decide(root.left);
int right = decide(root.right);
if(left < 0 || right < 0 || Math.abs(left - right) > 1)
return -1;
return left > right ? left + 1 : right + 1;
}
}