[LeetCode] 643. Maximum Average Subarray I

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].

子数组最大平均数 I。

给定 n 个整数，找出平均数最大且长度为 k 的连续子数组，并输出该最大平均数。

这道题的思路是滑动窗口，但是做法有点区别，不涉及two pointer。这道题比一般的滑动窗口题更简单，因为这道题的窗口长度是固定的K。所以我们先计算一下数组前K个数的和；然后从第 k + 1 个数开始，分别计算不同窗口里面数字的sum，并且记录一个最大的sum。最后再计算平均值。

时间O(n)

空间O(1)

Java实现

class Solution {
    public double findMaxAverage(int[] nums, int k) {
        long sum = 0;
        for (int i = 0; i < k; i++) {
            sum += nums[i];
        }

        long maxSum = sum;
        for (int i = k; i < nums.length; i++) {
            sum = sum - nums[i - k] + nums[i];
            maxSum = Math.max(maxSum, sum);
        }
        return 1.0 * maxSum / k;
    }
}

JavaScript实现

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
var findMaxAverage = function(nums, k) {
    let sum = 0;
    for (let i = 0; i < k; i++) {
        sum += nums[i];
    }
    let maxSum = sum;
    for (let i = k; i < nums.length; i++) {
        sum = sum - nums[i - k] + nums[i];
        maxSum = Math.max(maxSum, sum);
    }
    return 1.0 * maxSum / k;
};

LeetCode 题目总结