leetcode 1: balanced binary tree

Balanced Binary TreeOct 9 '12

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 everynode never differ by more than 1.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
 #include <algorithm>
 
class Solution {
public:
    int height( TreeNode *root) {
        if(root==NULL) return 0;
        
        return 1+ max( height(root->left), height(root->right) );
        
    }


    bool isBalanced(TreeNode *root) {
        if(root == NULL) return 1;
        
        if( isBalanced(root->left) && isBalanced(root->right) && abs( height(root->left) - height(root->right) ) <=1) {
            return 1;
        } else {
            return 0;
        }  
    }  
};

public class Solution {
    public boolean isBalanced(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        //input check
        if(root==null) return true;
        
        return balRec(root)!=-1;
    }
    
    private int balRec(TreeNode root) {
        if(root==null) return 0;
        
        int l = balRec(root.left);
        int r = balRec(root.right);
        
        if(l==-1 || r==-1) return -1;
        
        if( Math.abs(l-r)>1) {
            return -1;
        } else {
            return Math.max(l, r) +1;
        }   
    }   
}

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isBalanced(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        //input check
        if(root==null) return true;
        
        return balRec(root)!=-1;
    }
    
    private int balRec(TreeNode root) {
        if(root==null) return 0;
        
        int l = balRec(root.left);
        int r = balRec(root.right);
        
        if(l==-1 || r==-1) return -1;
        
        if( Math.abs(l-r)>1) {
            return -1;
        } else {
            return Math.max(l, r) +1;
        }   
    }   
}