C++几行直接解决

算法

直接用高度h，平衡二叉树递归满足1、左右子树是平衡的
                               2、左子树-右子树高度的绝对值<2

时间复杂度

o(n)

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        if(!root) return true;
        return isBalanced(root->left)&&isBalanced(root->right)&&abs(h(root->left)-h(root->right))<2;
    }
    int h(TreeNode *bt)
    {
        if(!bt)return 0;
        return max(h(bt->left),h(bt->right))+1;
    }
};