[Leetcode] Convert Sorted Array to Binary Search Tree

题目链接在此

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

基于一个有序数组，建立BST。

直观的做法：取数组中点作为根，左侧数组作为左子树，右侧数组作为右子树，不断递归地建树。

struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution {
public:
TreeNode* sortedArrayToBST(vector<int>& nums) {
return buildTree(nums, 0, nums.size() - 1);
}
private:
TreeNode* buildTree(vector<int>& nums, int low, int high) {
TreeNode* root = NULL;
if (low <= high) {
root = new TreeNode(nums[(low + high) / 2]);
root->left = buildTree(nums, low, (low + high) / 2 - 1);
root->right = buildTree(nums, (low + high) / 2 + 1, high);
}
return root;
}
};