Solution.java

/**
 * @author Anonymous
 * @since 2019/12/10
 */

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private boolean isBalanced;

    /**
     * 判断是否是平衡二叉树
     *
     * @param root 二叉树根结点
     * @return 是否是平衡二叉树
     */
    public boolean isBalanced(TreeNode root) {
        if (root == null) {
            return true;
        }
        isBalanced = true;
        treeDepth(root);
        return isBalanced;
    }

    private int treeDepth(TreeNode root) {
        if (root == null || !isBalanced) {
            return 0;
        }
        int lDepth = treeDepth(root.left);
        int rDepth = treeDepth(root.right);
        if (Math.abs(lDepth - rDepth) > 1) {
            isBalanced = false;
        }
        return 1 + Math.max(lDepth, rDepth);

    }
}