[Swift]LeetCode643. 子数组最大平均数 I | Maximum Average Subarray I

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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].

---

 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。

示例 1:

输入: [1,12,-5,-6,50,3], k = 4
输出: 12.75
解释: 最大平均数 (12-5-6+50)/4 = 51/4 = 12.75 

注意:

1. 1 <= k <= n <= 30,000。
2. 所给数据范围 [-10,000，10,000]。

---

Runtime: 1000 ms

Memory Usage: 20.1 MB

class Solution {
    func findMaxAverage(_ nums: [Int], _ k: Int) -> Double {
        var arr = nums[0..<k]
        var sum:Int = arr.reduce(0,+)
        var res:Int = sum
        for i in k..<nums.count
        {
            sum += nums[i] - nums[i - k]
            res = max(res, sum)
        }
        return Double(res) / Double(k)
    }
}

---

1016ms

class Solution {
    func findMaxAverage(_ nums: [Int], _ k: Int) -> Double {
        let count = nums.count
        var nums = nums
        var maxKTotal = 0
        
        for index in 0..<count {
            nums[index] += index > 0 ? nums[index - 1] : 0
            if index + 1 == k {
                maxKTotal = nums[index]
            } else if index + 1 > k {
                maxKTotal = max(maxKTotal, nums[index] - nums[index - k])
            }
        }
        return Double(maxKTotal) / Double(k)
    }
}

---

1148ms

class Solution {
    func findMaxAverage(_ nums: [Int], _ k: Int) -> Double {
        var maxSum = Int.min
        var current = 0
        
        for i in 0 ..< nums.count {
            if i < k {
                current += nums[i]
            } else {
                maxSum = max(current, maxSum)
                current += nums[i] - nums[i - k]
            }
        }
        maxSum = max(current, maxSum)
        return Double(maxSum) / Double(k)
    }
}

---

1168ms

class Solution {
    func findMaxAverage(_ nums: [Int], _ k: Int) -> Double {
        if (nums.count <= k) {
            return Double(nums.reduce(0,+))/Double(k)
        }
        
        var prev = nums[0..<k].reduce(0,+); var prevMax = prev
        for index in k..<nums.count {
            let tmp = nums[index] - nums[index-k] + prev
            prev = tmp
            prevMax = max(prevMax,tmp)
        }        
        return Double(prevMax)/Double(k)
    }
}

---

1560ms

lass Solution {
    func findMaxAverage(_ nums: [Int], _ k: Int) -> Double {
        var i = 0
        var sum = 0
        var temp = 0
        for item in nums {
            sum += item
            if i < k {
                temp = sum
            } else {
                sum -= nums[i-k]
                if temp < sum {
                    temp = sum
                }
            }
            i += 1
        }
        
        return Double(temp)/Double(k)
    }
}

---

1736ms

class Solution {
    func findMaxAverage(_ nums: [Int], _ k: Int) -> Double {
        guard nums.count >= k else {
            return 0.0
        }
        var sum = 0
        var m = 0
        for i in 0..<k {
            sum += nums[i]
        }
        m = sum
        for j in k..<nums.count {
            sum -= nums[j-k]
            sum += nums[j]
            m = max(m, sum)
        }
        return Double(m)/Double(k)
    }
}