// Convert Sorted Array to Binary Search Tree
class Solution {
public:
  TreeNode *sortedArrayToBST(vector<int> &a) {
    return f(a, 0, a.size());
  }
  TreeNode *f(vector<int> &a, int l, int h) {
    if (l == h) return NULL;
    int m = l+h >> 1;
    TreeNode *x = new TreeNode(a[m]);
    x->left = f(a, l, m);
    x->right = f(a, m+1, h);
    return x;
  }
};