[Leetcode] convert sorted array to binary search tree

Posted 2020-09-26 王大咩的图书馆

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

题意：将已排序的数组转成高度平衡的搜索二叉树。

思路：这题和Convert sorted list to binary search tree 方法一的处理方法基本一样，不同是数组可以直接访问某个元素，而链表不可以。代码如下：

 1 /**
 2  * Definition for binary tree
 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> &num) 
13     {
14         if(num.size()==0)   return NULL;
15         return reBulidBST(num,0,num.size()-1);
16     }
17     TreeNode *reBulidBST(vector<int> &num,int beg,int end)
18     {
19         if(beg>end) return NULL;
20 
21         int mid=beg+(end-beg+1)/2;
22         TreeNode *root=new TreeNode(num[mid]);
23         root->left=reBulidBST(num,beg,mid-1);
24         root->right=reBulidBST(num,mid+1,end);
25 
26         return root;
27     }
28 };