1746-MaximumSubarraySumAfterOneOperation.go

package main

// 1746. Maximum Subarray Sum After One Operation
// You are given an integer array nums. 
// You must perform exactly one operation where you can replace one element nums[i] with nums[i] * nums[i]. 

// Return the maximum possible subarray sum after exactly one operation. The subarray must be non-empty.

// Example 1:
// Input: nums = [2,-1,-4,-3]
// Output: 17
// Explanation: You can perform the operation on index 2 (0-indexed) to make nums = [2,-1,16,-3]. Now, the maximum subarray sum is 2 + -1 + 16 = 17.

// Example 2:
// Input: nums = [1,-1,1,1,-1,-1,1]
// Output: 4
// Explanation: You can perform the operation on index 1 (0-indexed) to make nums = [1,1,1,1,-1,-1,1]. Now, the maximum subarray sum is 1 + 1 + 1 + 1 = 4.

// Constraints:
//     1 <= nums.length <= 10^5
//     -10^4 <= nums[i] <= 10^4

import "fmt"

func maxSumAfterOperation(nums []int) int {
    res, a, b := 0, 0, 0 
    max := func (x, y int) int { if x > y { return x; }; return y; }
    for _, v := range nums {
        a, b = max(0, a + v), max(0, max(v + b, a + v * v))
        res = max(res, max(a, b))
    }
    return res
}

func main() {
    // Example 1:
    // Input: nums = [2,-1,-4,-3]
    // Output: 17
    // Explanation: You can perform the operation on index 2 (0-indexed) to make nums = [2,-1,16,-3]. Now, the maximum subarray sum is 2 + -1 + 16 = 17.
    fmt.Println(maxSumAfterOperation([]int{2,-1,-4,-3})) // 17
    // Example 2:
    // Input: nums = [1,-1,1,1,-1,-1,1]
    // Output: 4
    // Explanation: You can perform the operation on index 1 (0-indexed) to make nums = [1,1,1,1,-1,-1,1]. Now, the maximum subarray sum is 1 + 1 + 1 + 1 = 4.
    fmt.Println(maxSumAfterOperation([]int{1,-1,1,1,-1,-1,1})) // 4
}