【leetcode】Convert Sorted Array to Binary Search Tree

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

采用二分递归。

 1 class Solution {
 2 public:
 3     TreeNode *createTree(vector<int> &num,int begin,int end)
 4     {
 5         if(begin>end) return NULL;
 6         int mid=(begin+end)/2;
 7         TreeNode *root=new TreeNode(num[mid]);
 8         root->left=createTree(num,begin,mid-1);
 9         root->right=createTree(num,mid+1,end);
10         return root;
11     }
12
13     TreeNode *sortedArrayToBST(vector<int> &num) {
14         if(num.size()==0) return NULL;
15         return createTree(num,0,num.size()-1);
16     }
17 };