LeetCode 643. Maximum Average Subarray I

Description

Given an array consisting of n integers, find the contiguous subarray of given length k that has the maximum average value. And you need to output the maximum average value.

Example:
Input: [1,12,-5,-6,50,3], k = 4
Output: 12.75
Explanation: Maximum average is (12-5-6+50)/4 = 51/4 = 12.75

Note:
1 <= k <= n <= 30,000.
Elements of the given array will be in the range [-10,000, 10,000].

Analysis

题目希望你从数组中找出连续k个数组成的子数组，要求其平均数最大，其实就是操作滑动距离为1的滑动窗，但写代码时要注意以下几点：

• 此处，平均数最大等价于和最大，所以中途运算是不需要算平均数，只需要在最后结果处除以k。
• 由于数组中存储的是整数，所以直接拿和除以k得到的数字还是整数，要对求得的和进行强制类型转换。
• 由于前后滑动窗之间大部分元素相同，所以没必要大量重复运动（会超时）。窗口滑动，只需要将离开窗口的元素减掉，再将新进入窗口的元素加上即可。

Code

class Solution {public:    double findMaxAverage(vector<int>& nums, int k) {        int  result, sum = 0;        for (int i = 0; i < k; i++)            sum += nums[i];        result = sum;        for (int i = 1; i <= nums.size() - k; i++){            sum = sum - nums[i - 1] + nums[i + k - 1];            result = max(sum, result);        }        return (double)result / k;    }};

Appendix

• Link: https://leetcode.com/problems/maximum-average-subarray-i/
• Run Time: 192ms