110. Balanced Binary Tree

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.

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初看题，以为是平衡一棵二叉树，结果是判断一棵二叉树是否是平衡二叉树，这样的话，我们只需要知道每个节点的高度就可以了。

代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
int heightForNode(struct TreeNode *node){
    if(node ==NULL){
        return 0;
    }
    if(node->left==NULL&&node->right==NULL){
        return 1;
    }
    int left_height=heightForNode(node->left);
    int right_height=heightForNode(node->right);
    return (left_height>right_height?left_height:right_height)+1;
}
bool isBalanced(struct TreeNode* root) {
 if(root==NULL) return true;
 if(abs(heightForNode(root->left)-heightForNode(root->right))<=1&&isBalanced(root->left)&&isBalanced(root->right))
 return true;
 return false;
    
}