原题链接: https://oj.leetcode.com/problems/balanced-binary-tree/

public boolean isBalanced(TreeNode root) {
    if (root == null) return true;

    int left = maxDepth(root.left);
    int right = maxDepth(root.right);

    if (Math.abs(left - right) > 1) {
        return false;
    }

    return isBalanced(root.left) && isBalanced(root.right);
}

public int maxDepth(TreeNode root) {
    if (root == null) return 0;

    if (root.left == null && root.right == null) {
        return 1;
    }

    return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
}