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Balanced Binary Tree

描述

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.

分析

代码

// Balanced Binary Tree
// 时间复杂度O(n),空间复杂度O(logn)
public class Solution {
public boolean isBalanced (TreeNode root) {
return balancedHeight (root) >= 0;
}

/**
* Returns the height of `root` if `root` is a balanced tree,
* otherwise, returns `-1`.
*/
private static int balancedHeight (TreeNode root) {
if (root == null) return 0; // 终止条件

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

if (left < 0 || right < 0 || Math.abs(left - right) > 1) return -1; // 剪枝

return Math.max(left, right) + 1; // 三方合并
}
}