LeetCode - Convert Sorted Array to Binary Search Tree

给出一个已排序的数组，将其转化为二叉查找树（BST）。

思路：取数组中间元素为根结点的value，则数组左侧、右侧分别为BST的左子树、右子树。递归可求解。代码如下：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode *convert(int *start, int *end)
    {
        if (start > end)
            return NULL;
        int *mid = start + (end - start)/2;
        TreeNode *node = (TreeNode *)malloc(sizeof(TreeNode));
        node->val = *mid;
        node->left = convert(start, mid-1);
        node->right = convert(mid+1, end);
        return node;
    }
    TreeNode *sortedArrayToBST(vector<int> &num)
    {
        if (num.size() == 0)
            return NULL;
        return convert(&num[0], &num[num.size()-1]);
    }
};