[Leetcode] Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

哎，又是被指针坑了，指针作为函数的参数传递时，在函数体内可以修改指针所指的内容，但是不有修改指针本身，所以一时是运行时错误，这里要用指针的引用TreeNode *&，问题得解。算法没什么好说的，递归求解，每次取传入列表的中位数为节点的值。

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
void buildTree(TreeNode *&root, vector<int> &num, int l, int h) {
if (l <= h) {
int mid = (l + h) / 2;
root = new TreeNode(num[mid]);
buildTree(root->left, num, l, mid - 1);
buildTree(root->right, num, mid + 1, h);
}
}

TreeNode *sortedArrayToBST(vector<int> &num) {
if (num.size() < 1) {
return NULL;
}
TreeNode *root;
buildTree(root, num, 0, num.size() - 1);
return root;
}
};