[LeetCode By Go 90]643. Maximum Average Subarray I

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

解题思路

计算所有k个连续数的和，求得最大值，平均值
一共有n-k+1个连续k个数，每次用累加求k个连续数的和，需要计算(n-k+1)k次，时间复杂度为O(nk)
考虑到下一个连续k个数的和可以根据上一个连续值的和推出，

sum + nums[j] - nums[j-k]
需要计算(n-k+1)*2次，时间复杂度降为O(n)

代码

func findMaxAverage(nums []int, k int) float64 {
    len1 := len(nums)
    var sum, maxSum int
    for i := 0; i < k; i++ {
        sum += nums[i]
    }
    maxSum = sum 
    fmt.Printf("sum:%+v\n", sum)
    for j := k; j < len1; j++ {
        sum =  sum + nums[j] - nums[j-k]
        if maxSum < sum {
            maxSum = sum 
        }
        fmt.Printf("j:%+v, sum:%+v\n", j, sum)
    }
    
    return float64(maxSum) / float64(k)
}