leetcode[108]Convert Sorted Array to Binary Search Tree

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:

void creatTree(TreeNode *&root,vector<int> &num,int left,int right)

{

    if(left>right)return;

    int mid=(left+right)/2;

    root=new TreeNode(num[mid]);

    creatTree(root->left,num,left,mid-1);

    creatTree(root->right,num,mid+1,right);

}

TreeNode *sortedArrayToBST(vector<int> &num) 

{

    TreeNode *root=NULL;

    creatTree(root,num,0,num.size()-1);

    return root;

}

};