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

Moving window solution

Just be noticing that you don’t need to calculate the “average” until you return the result.

public class Solution {
    public double findMaxAverage(int[] nums, int k) {
        /**
        * Moving window solution
        * @timeComplexity:  O(n)
        * @spaceComplexity: O(1)
        * @runtime:         22ms
        */
        if (k > nums.length)    return 0;
        
        int windowSum = 0;
        int maxSum = 0;
        for (int i=0; i<k; i++) {
            windowSum += nums[i];
        }
        maxSum = windowSum;
        int i = 0;
        for (int j = k; j < nums.length; j++) {
            windowSum = windowSum - nums[i] + nums[j];
            i++;
            maxSum = Math.max(maxSum, windowSum);
        }
        
        return (double) maxSum/k;
    }
}

imgRuntime: 22ms