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.

/**
 * Definition for a binary tree node.
 * 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;
        int depthL = getDepth(root.left);
        int depthR = getDepth(root.right);
        if (Math.abs(depthL - depthR) > 1) return false;
        return isBalanced(root.left) && isBalanced(root.right);
    }

    private int getDepth(TreeNode root) {
        if (root == null) return 0;
        int l = getDepth(root.left);
        int r = getDepth(root.right);
        return (l > r ? l : r) + 1;
        /**
        // Should add the following two lines.
        if (root.left != null && root.right != null) return Math.max(getDepth(root.left), getDepth(root.right)) + 1;
        else if (root.left != null) return getDepth(root.left) + 1;
        else if (root.right != null) return getDepth(root.right) + 1;
        else return 1;
        */
    }

}
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