title: Balanced Binary Tree
tags:
- balanced-binary-tree
- No.110
- simple
- tree
- depth-first-search
- recursive
Description
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.
Example 1:
Given the following tree [3,9,20,null,null,15,7]:
3
/ \
9 20
/ \
15 7
Return true.
Example 2:
Given the following tree [1,2,2,3,3,null,null,4,4]:
1
/ \
2 2
/ \
3 3
/ \
4 4
Return false.
Corner Cases
- empty root
Solutions
Queue
Recursively solve height and compare them. Running time is O(V) for dfs.
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
private boolean flag = true;
public boolean isBalanced(TreeNode root) {
if (root == null) {return true;}
int hl = h(root.left);
int hr = h(root.right);
flag = flag & (hl == hr || hl == hr + 1 || hl == hr - 1);
return flag;
}
private int h(TreeNode x) {
if (x == null) {return 0;}
int hl = h(x.left);
int hr = h(x.right);
flag = flag & (hl == hr || hl == hr + 1 || hl == hr - 1);
return (hl > hr) ? hl + 1 : hr + 1;
}
}
