[Leetcode]108. Convert Sorted Array to Binary Search Tree (C++)

题目描述

题目链接：108. Convert Sorted Array to Binary Search Tree

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 every node never differ by more than 1.

例子

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

解题思路

由于已经给定了一个排序数组，所以构建高度平衡二叉搜索树比较简单，只需要取中间值作为根结点，对于两侧子数组进行递归操作，返回的根结点分别作为左右子树即可，代码如下：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
 * right(right) {}
 * };
 */
#include <vector>

class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return buildTree(nums, 0, nums.size() - 1);
    }

private:
    TreeNode* buildTree(std::vector<int>& nums, int begin, int end) {
        if (begin > end) {
            return nullptr;
        }

        int mid = (begin + end) / 2;
        TreeNode* root = new TreeNode(nums[mid]);
        root->left = buildTree(nums, begin, mid - 1);
        root->right = buildTree(nums, mid + 1, end);
        return root;
    }
};

时间复杂度: O(n)
空间复杂度: O(n) – n 个节点作为新的二叉搜索树

GitHub 代码同步地址： 108.ConvertSortedArrayToBinarySearchTree.cpp

其他题目： GitHub: Leetcode-C++-Solution 博客： Leetcode-Solutions