LeetCode題解：Convert Sorted Array to Binary Search Tree

Convert Sorted Array to Binary Search Tree
Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
思路：
給定一個區間[left, right]，取其中值mid=(left+right)/2對應的元素作為二叉樹的根。二叉樹的左子樹根的值為對[left, mid-1]繼續操作的結果，右子樹類似。
題解：

/** * 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* generateBST(int left, int right, vector<int>& num)    {        if (left > right)            return nullptr;        else if (left == right)            return new TreeNode(num[left]);        else        {            int mid = (left + right) / 2;            TreeNode* node = new TreeNode(num[mid]);            node->left = generateBST(left, mid - 1, num);            node->right = generateBST(mid + 1, right, num);            return node;        }    }    TreeNode *sortedArrayToBST(vector<int> &num) {        return generateBST(0, num.size() - 1, num);    }};