【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。

class Solution {
public:
    TreeNode *createTree(vector<int> &num,int begin,int end)
    {
        if(begin>end) return NULL;
        int mid=(begin+end)/2;
        TreeNode *root=new TreeNode(num[mid]);
        root->left=createTree(num,begin,mid-1);
        root->right=createTree(num,mid+1,end);
        return root;
    }

    TreeNode *sortedArrayToBST(vector<int> &num) {
        if(num.size()==0) return NULL;
        return createTree(num,0,num.size()-1);
    }
};