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

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 * int val;
 * struct TreeNode *left;
 * struct TreeNode *right;
 * };
 */
struct TreeNode* build(int* nums,int st,int ed){
    struct TreeNode* r;
    if(st>ed)return NULL;
    int md = st+(ed-st)/2;
    r = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    r->val = nums[md];
    r->left = build(nums,st,md-1);
    r->right = build(nums,md+1,ed);
    return r;
}
struct TreeNode* sortedArrayToBST(int* nums, int numsSize) {
    return build(nums,0,numsSize-1);
}