algorithms/leetcode/3026-MaximumGoodSubarraySum.go at master · freewu/algorithms · GitHub

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package main

// 3026. Maximum Good Subarray Sum
// You are given an array nums of length n and a positive integer k.

// A subarray of nums is called good if the absolute difference between its first and last element is exactly k,
// in other words, the subarray nums[i..j] is good if |nums[i] - nums[j]| == k.

// Return the maximum sum of a good subarray of nums.
// If there are no good subarrays, return 0.

// Example 1:
// Input: nums = [1,2,3,4,5,6], k = 1
// Output: 11
// Explanation: The absolute difference between the first and last element must be 1 for a good subarray. All the good subarrays are: [1,2], [2,3], [3,4], [4,5], and [5,6]. The maximum subarray sum is 11 for the subarray [5,6].

// Example 2:
// Input: nums = [-1,3,2,4,5], k = 3
// Output: 11
// Explanation: The absolute difference between the first and last element must be 3 for a good subarray. All the good subarrays are: [-1,3,2], and [2,4,5]. The maximum subarray sum is 11 for the subarray [2,4,5].

// Example 3:
// Input: nums = [-1,-2,-3,-4], k = 2
// Output: -6
// Explanation: The absolute difference between the first and last element must be 2 for a good subarray. All the good subarrays are: [-1,-2,-3], and [-2,-3,-4]. The maximum subarray sum is -6 for the subarray [-1,-2,-3].

// Constraints:
//     2 <= nums.length <= 10^5
//     -10^9 <= nums[i] <= 10^9
//     1 <= k <= 10^9

import "fmt"

func maximumSubarraySum(nums []int, k int) int64 {
    res, sum, n := int(-1e18), 0, len(nums)
    mp := make(map[int]int, n)
    for i := 0; i < n; i++ {
        sum += nums[i]
        if v, ok := mp[nums[i] + k]; ok && res < sum - v {
            res = sum - v
        }
        if  v, ok := mp[nums[i] - k]; ok && res < sum - v {
            res = sum - v
        }

        if v, ok := mp[nums[i]]; !ok || (ok && sum - nums[i] < v) {
            mp[nums[i]] = sum - nums[i]
        }
    }
    if res == -1e18 { return 0 }
    return int64(res)
}

func maximumSubarraySum1(nums []int, k int) int64 {
    res, sum := int64(-1 << 63), 0
    mp := make(map[int]int)
    max := func (x, y int64) int64 { if x > y { return x; }; return y; }
    for i := 0; i < len(nums); i++ {
        num := nums[i]
        if v, ok := mp[num]; !ok || sum < v { // 记录上一步，没有则初始化
            mp[num] = sum
        }
        sum += num
        // 找+-k的差值
        if v, ok := mp[num - k]; ok {
            res = max(res, int64(sum - v))
        }
        if v, ok := mp[num + k]; ok {
            res = max(res, int64(sum - v))
        }
    }
    if res == int64(-1 << 63) { res = 0 }
    return res
}

func main() {
    // Example 1:
    // Input: nums = [1,2,3,4,5,6], k = 1
    // Output: 11
    // Explanation: The absolute difference between the first and last element must be 1 for a good subarray. All the good subarrays are: [1,2], [2,3], [3,4], [4,5], and [5,6]. The maximum subarray sum is 11 for the subarray [5,6].
    fmt.Println(maximumSubarraySum([]int{1,2,3,4,5,6}, 1)) // 11
    // Example 2:
    // Input: nums = [-1,3,2,4,5], k = 3
    // Output: 11
    // Explanation: The absolute difference between the first and last element must be 3 for a good subarray. All the good subarrays are: [-1,3,2], and [2,4,5]. The maximum subarray sum is 11 for the subarray [2,4,5].
    fmt.Println(maximumSubarraySum([]int{-1,3,2,4,5}, 3)) // 11
    // Example 3:
    // Input: nums = [-1,-2,-3,-4], k = 2
    // Output: -6
    // Explanation: The absolute difference between the first and last element must be 2 for a good subarray. All the good subarrays are: [-1,-2,-3], and [-2,-3,-4]. The maximum subarray sum is -6 for the subarray [-1,-2,-3].
    fmt.Println(maximumSubarraySum([]int{-1,-2,-3,-4}, 2)) // -6

    fmt.Println(maximumSubarraySum([]int{1,2,3,4,5,6,7,8,9}, 2)) // 24
    fmt.Println(maximumSubarraySum([]int{9,8,7,6,5,4,3,2,1}, 2)) // 24

    fmt.Println(maximumSubarraySum1([]int{1,2,3,4,5,6}, 1)) // 11
    fmt.Println(maximumSubarraySum1([]int{-1,3,2,4,5}, 3)) // 11
    fmt.Println(maximumSubarraySum1([]int{-1,-2,-3,-4}, 2)) // -6
    fmt.Println(maximumSubarraySum1([]int{1,2,3,4,5,6,7,8,9}, 2)) // 24
    fmt.Println(maximumSubarraySum1([]int{9,8,7,6,5,4,3,2,1}, 2)) // 24
}