2014.1.8 04:09

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.

Solution:

　　Just do as the problem says, calculate the heights and check if they meet the requirement.

　　Time complexity is O(n), where n is the number of nodes in the tree. Space complexity is O(1).

Accepted code:

1 // 1AC, good~ 2 /** 3  * Definition for binary tree 4  * struct TreeNode { 5  *     int val; 6  *     TreeNode *left; 7  *     TreeNode *right; 8  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 9  * };10  */11 class Solution {12 public:13     bool isBalanced(TreeNode *root) {14         // IMPORTANT: Please reset any member data you declared, as15         // the same Solution instance will be reused for each test case.16         if(root == nullptr){17             return true;18         }19         20         return myabs(treeHeight(root->left) - treeHeight(root->right)) <= 1 && isBalanced(root->left) && isBalanced(root->right);21     }22 private:23     const int &myabs(const int &num) {24         return (num >= 0 ? num : -num);25     }26     27     const int &mymax(const int &x, const int &y) {28         return (x > y ? x : y);29     }30     31     int treeHeight(TreeNode *root) {32         if(root == nullptr){33             return 0;34         }else{35             return mymax(treeHeight(root->left), treeHeight(root->right)) + 1;36         }37     }38 };