C++实现LeetCode(108.将有序数组转为二叉搜索树)

时间:2021-08-09 00:47:01

[LeetCode] 108.Convert Sorted Array to Binary Search Tree 将有序数组转为二叉搜索树

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

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of everynode never differ by more than 1.

Example:

Given the sorted array: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
/ \
-3   9
/   /
-10  5 

这道题是要将有序数组转为二叉搜索树,所谓二叉搜索树,是一种始终满足左<根<右的特性,如果将二叉搜索树按中序遍历的话,得到的就是一个有序数组了。那么反过来,我们可以得知,根节点应该是有序数组的中间点,从中间点分开为左右两个有序数组,在分别找出其中间点作为原中间点的左右两个子节点,这不就是是二分查找法的核心思想么。所以这道题考的就是二分查找法,代码如下:

解法一:

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return helper(nums, 0 , (int)nums.size() - 1);
    }
    TreeNode* helper(vector<int>& nums, int left, int right) {
        if (left > right) return NULL;
        int mid = left + (right - left) / 2;
        TreeNode *cur = new TreeNode(nums[mid]);
        cur->left = helper(nums, left, mid - 1);
        cur->right = helper(nums, mid + 1, right);
        return cur;
    }
};

我们也可以不使用额外的递归函数,而是在原函数中完成递归,由于原函数的参数是一个数组,所以当把输入数组的中间数字取出来后,需要把所有两端的数组组成一个新的数组,并且分别调用递归函数,并且连到新创建的cur结点的左右子结点上面,参见代码如下:

解法二:

?
1
2
3
4
5
6
7
8
9
10
11
12
class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        if (nums.empty()) return NULL;
        int mid = nums.size() / 2;
        TreeNode *cur = new TreeNode(nums[mid]);
        vector<int> left(nums.begin(), nums.begin() + mid), right(nums.begin() + mid + 1, nums.end());
        cur->left = sortedArrayToBST(left);
        cur->right = sortedArrayToBST(right);
        return cur;
    }
};

类似题目:

Convert Sorted List to Binary Search Tree

参考资料:

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/discuss/35220/My-Accepted-Java-Solution

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/discuss/35394/6-lines-Java-Accepted-Solution

到此这篇关于C++实现LeetCode(108.将有序数组转为二叉搜索树)的文章就介绍到这了,更多相关C++实现将有序数组转为二叉搜索树内容请搜索服务器之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持服务器之家!

原文链接:https://www.cnblogs.com/grandyang/p/4295245.html