LeetCode 643. Maximum Average Subarray I

原题链接在这里：https://leetcode.com/problems/maximum-average-subarray-i/description/

题目：

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 1:

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

题解：

维护长度为k的sliding window的最大sum.

Note: In Java, Double.MIN_VALUE is the smallest positive double value, thus here use -Double.MAX_VALUE.

Time Complexity: O(nums.length). Space: O(1).

AC Java:

class Solution {
    public double findMaxAverage(int[] nums, int k) {
        double res = -Double.MAX_VALUE;
        double sum = 0;
        for(int i = 0; i < nums.length; i++){
            sum += nums[i];
            if(i >= k - 1){
                res = Math.max(res, sum / k);
                sum -= nums[i - k + 1];
            }
        }

        return res;
    }
}