Leetcode: Convert Sorted Array to Binary Search Tree

http://oj.leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int leftCnt(int total){        if(total==1) return 0;        int left=1;        while(1){            int right=total-1-left;            if(left==right) break;            if(left>right){                right=left/2;                left=min(left,total-1-right);                break;            }            left=left*2+1;        }        return left;    }    void makeNode(TreeNode* &root, vector<int> &num, int start, int end){        if(start==end){            root=new TreeNode(num[start]);        }        else if(start<end){            int left=leftCnt(end-start+1);            int right=end-start-left;            root=new TreeNode(num[start+left]);            makeNode(root->left,num,start,start+left-1);            if(right>0) makeNode(root->right,num,start+left+1,end);        }        else            root=NULL;    }    TreeNode* sortedArrayToBST(vector<int> &num) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        TreeNode *root=NULL;        makeNode(root,num,0,num.size()-1);        return root;    }};