【Lintcode]177.Convert Sorted Array to Binary Search Tree With Minimal Height

题目：

Given a sorted (increasing order) array, Convert it to create a binary tree with minimal height.

Example

Given [1,2,3,4,5,6,7], return

     4
   /     2     6
 / \    / 1   3  5   7

题解：

Solution 1 ()

class Solution {
public:
    TreeNode *sortedArrayToBST(vector<int> &A) {
        if (A.size() == 0) return nullptr;

        return buildTree(A, 0, A.size() - 1);
    }
    TreeNode* buildTree(vector<int>&A, int begin, int end) {
        if (begin > end) {
            return nullptr;
        }
        int mid = begin + (end - begin) / 2;
        TreeNode* root = new TreeNode(A[mid]);
        root->left = buildTree(A, begin, mid - 1);
        root->right = buildTree(A, mid + 1, end);
        return root;
    }
};