convertSortedArrayToBinarySearchTree.cpp

// Source : https://oj.leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
// Author : Hao Chen
// Date   : 2014-06-23

/********************************************************************************** 
* 
* Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
*               
**********************************************************************************/

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode *sortedArrayToBST(vector<int> &num) {
        if(num.size()==0){
            return NULL;
        }
        if(num.size()==1){
            return new TreeNode(num[0]);
        }
        int mid = num.size()/2;
        
        TreeNode *node = new TreeNode(num[mid]);
        
        vector<int>::const_iterator first;
        vector<int>::const_iterator last;

        first = num.begin();
        last = num.begin()+mid;
        vector<int> v(first, last);
        node->left = sortedArrayToBST(v);
        
        if (mid==num.size()-1){
            node->right = NULL;
        }else{
            first = num.begin()+mid+1;
            last = num.end();
            vector<int> v(first, last);
            node->right = sortedArrayToBST(v);
        }
        return node;
    }
};