/**
knakul853
 */
class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        int n = (int)nums.size();

        if( !n ) return NULL;
       return dfs(nums, 0, n-1);

    }

    TreeNode* dfs( vector<int>&nums, int st, int end )
    {
        if(st > end) return NULL;
        TreeNode* root = new TreeNode(nums[(st+end)/2]);
        int md = ( st + end )/2;

         root->left = dfs( nums, st, md-1);
         root->right = dfs(nums, md+1, end);

         return root;

    }
};