LeetCode 108. Convert Sorted Array to Binary Search Tree

给定升序数组，构造平衡查找二叉树。

代码：

class Solution
{
public:
TreeNode *sortedArrayToBST(vector<int> &num)
{
return gao(num, 0, num.size());
}
private:
TreeNode *gao(vector<int>& num, int begin, int end)
{
if (begin >= end)
{
return NULL;
}
TreeNode *node = new TreeNode(num[ (end-begin)/2 ]);
node->left = gao(num, begin, (end-begin)/2-1);
node->right = gao(num, (end-begin)/2+1, end);
return node;
}
};