leetcode/BalancedBinaryTree.java at master · nbjsw/leetcode · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
/**
 * 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) {
        int[] h = new int[1];
        return isBalancedHelper(root, h);
    }

    //This is a O(n) solution, avoiding revisiting the same node
    private boolean isBalancedHelper(TreeNode root, int[] h) {
        boolean l; // Is left subtree balanced?
        boolean r; // Is right subtree balanced?

        int[] lh = new int[1]; // height of left subtree
        int[] rh = new int[1]; // height of right subtree

        if (null == root) {
            h[0] = 0;
            return true;
        }

        l = isBalancedHelper(root.left, lh);
        r = isBalancedHelper(root.right, rh);

        if (l == false || r == false) return false;

        if ( (lh[0] - rh[0]) > 1 || (rh[0] - lh[0]) > 1 ) return false;

        h[0] = Math.max(lh[0], rh[0]) + 1;

        return true;
    }
}