[LeetCode] 643. Maximum Average Subarray I

轉自LeetCode

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].

<Solution>

想法如下

• 可以不用管平均，只要找到指定長度下，總和最大的 subarray 就是所求

• 利用 slicing window 的概念，先計算 1 到 k 這個 subarray 的和(sum)，之後如果要計算 2 到 k+1 的和，就是 sum + nums[k+1] - nums[1]

code 如下

Java(參考解答)

	class Solution {
	public double findMaxAverage(int[] nums, int k) {
	double sum = 0;
	for(int i = 0; i < k; i++) {
	sum += nums[i];
	}
	double ans = sum;
	for(int i = k; i < nums.length; i++) {
	sum += nums[i] - nums[i-k];
	ans = Math.max(ans, sum);
	}
	return ans / k;
	}
	}

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