1.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.

2.分析

先判断左子树和右子树是否为平衡，然后判断左右子树的高度差是否小于等于1。

3.代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
 
bool isChildBalanced(struct TreeNode* root, int* height) {
    if (NULL == root) {
        *height = 0;
        return true;
    }
    int leftHeight, rightHeight;
    bool left = isChildBalanced(root->left, &leftHeight);
    bool right = isChildBalanced(root->right, &rightHeight);
    *height = leftHeight >= rightHeight ? leftHeight + 1 : rightHeight + 1;
    bool balance = leftHeight >= rightHeight ? leftHeight - rightHeight <= 1 : rightHeight - leftHeight <=1;
    return balance & left & right;
}

bool isBalanced(struct TreeNode* root) {
    if (NULL == root) return true;
    int height;
    return isChildBalanced(root, &height);
}