[LeetCode]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.

BST的规则就是左<根<右，所有这道题和二分搜索差不多。

注意处理的细节，是的无论奇数个num还是偶数个num都适用。

适用递归实现。

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     TreeNode* sortedArrayToBST(vector<int>& nums) {
13         return createTree(nums,0,nums.size()-1);
14     }
15     TreeNode* createTree(vector<int>& nums,int left,int right)
16     {
17         if(left>right) return NULL;
18         int mid = (left+right)/2;
19         TreeNode* leftTree = createTree(nums,left,mid-1);
20         TreeNode* rightTree = createTree(nums,mid+1,right);
21         TreeNode* root = new TreeNode(nums[mid]);
22         root->left = leftTree;
23         root->right = rightTree;
24         return root;
25     }
26 };