[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;
    }
};