LeetCode

Balanced Binary Tree

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:

// 1AC, good~
/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode *root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(root == nullptr){
            return true;
        }
        
        return myabs(treeHeight(root->left) - treeHeight(root->right)) <= 1 && isBalanced(root->left) && isBalanced(root->right);
    }
private:
    const int &myabs(const int &num) {
        return (num >= 0 ? num : -num);
    }
    
    const int &mymax(const int &x, const int &y) {
        return (x > y ? x : y);
    }
    
    int treeHeight(TreeNode *root) {
        if(root == nullptr){
            return 0;
        }else{
            return mymax(treeHeight(root->left), treeHeight(root->right)) + 1;
        }
    }
};