LIKE CODING: LeetCode [110] Balanced Binary Tree

Sunday, February 22, 2015

LeetCode [110] Balanced Binary Tree

110. Balanced Binary Tree

Easy

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 left and right subtrees of every node differ in height by no more than 1.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: true

Example 2:

Input: root = [1,2,2,3,3,null,null,4,4]
Output: false

Example 3:

Input: root = []
Output: true

Constraints:

The number of nodes in the tree is in the range [0, 5000].
-104 <= Node.val <= 104

//C++: method1 18ms
/**
 * 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) {
        int len = 0;
        return dfs(root, len);
    }

    bool dfs(TreeNode* root, int &len){
        if(!root) return true;
        len++;
        int len_left = 0, len_right = 0;
        if(!dfs(root->left, len_left)) return false;
        if(!dfs(root->right, len_right)) return false;
        if(abs(len_left-len_right)>1) return false;
        len += max(len_left, len_right);
        return true;
    }
};

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isBalanced(TreeNode root) {
        return helper(root)>=0;
    }
    
    int helper(TreeNode node){
        if(node==null) return 0;
        int l = helper(node.left);
        if(l<0) return -1;
        int r = helper(node.right);
        if(r<0) return -1;
        if(Math.abs(r-l)>1) return -1;
        return Math.max(l, r)+1;
    }
}

LIKE CODING

Sunday, February 22, 2015

LeetCode [110] Balanced Binary Tree

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