【leetcode】Convert Sorted Array to Binary Search Tree

Convert Sorted Array to Binary Search Tree

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

 

每次把中间元素当成根节点，递归即可

 

 1 /**

 2  * Definition for binary tree

 3  * struct TreeNode {

 4  *     int val;

 5  *     TreeNode *left;

 6  *     TreeNode *right;

 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 8  * };

 9  */

10 class Solution {

11 public:

12     TreeNode *sortedArrayToBST(vector<int> &num) {

13        

14         TreeNode *root=buildTree(num,0,num.size()-1);

15         return root;

16     }

17    

18    

19     TreeNode *buildTree(vector<int> &num,int l,int r)

20     {

21         if(l>r) return NULL;

22        

23         int mid=(l+r)/2;

24        

25         TreeNode *root=new TreeNode(num[mid]);

26         root->left=buildTree(num,l,mid-1);

27         root->right=buildTree(num,mid+1,r);

28        

29         return root;

30     }

31 };