LeetCode 108

108. Convert Sorted Array to Binary Search Tree
Easy

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

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example:

Given the sorted array: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / \
   -3   9
   /   /
 -10  5

1. /**
   
2.  * Definition for a binary tree node.
   
3.  * struct TreeNode {
   
4.  * int val;
   
5.  * struct TreeNode *left;
   
6.  * struct TreeNode *right;
   
7.  * };
   
8.  */
   
9. struct TreeNode* build(int* nums,int st,int ed){
   
10.     struct TreeNode* r;
    
11.     if(st>ed)return NULL;
    
12.     int md = st+(ed-st)/2;
    
13.     r = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    
14.     r->val = nums[md];
    
15.     r->left = build(nums,st,md-1);
    
16.     r->right = build(nums,md+1,ed);
    
17.     return r;
    
18. }
    
19. struct TreeNode* sortedArrayToBST(int* nums, int numsSize) {
    
20.     return build(nums,0,numsSize-1);
    
21. }