108. Convert Sorted Array to Binary Search Tree

Well, not much to say. Pretty straightforward DFS solution.

1:  /**  
2:   * Definition for a binary tree node.  
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>& nums) {  
13:      int n = nums.size();  
14:      return helper(nums, 0, n-1);  
15:    }  
16:    TreeNode *helper(vector<int> &nums, int s, int e) {  
17:      if (s > e) return NULL;  
18:      int mid = s + (e - s) / 2;  
19:      TreeNode *node = new TreeNode(nums[mid]);  
20:      node->left = helper(nums, s, mid-1);  
21:      node->right = helper(nums, mid+1, e);  
22:      return node;  
23:    }  
24:  };