2016-MaximumDifferenceBetweenIncreasingElements.go

package main

// 2016. Maximum Difference Between Increasing Elements
// Given a 0-indexed integer array nums of size n, 
// find the maximum difference between nums[i] and nums[j] (i.e., nums[j] - nums[i]), 
// such that 0 <= i < j < n and nums[i] < nums[j].

// Return the maximum difference. If no such i and j exists, return -1.

// Example 1:
// Input: nums = [7,1,5,4]
// Output: 4
// Explanation:
// The maximum difference occurs with i = 1 and j = 2, nums[j] - nums[i] = 5 - 1 = 4.
// Note that with i = 1 and j = 0, the difference nums[j] - nums[i] = 7 - 1 = 6, but i > j, so it is not valid.

// Example 2:
// Input: nums = [9,4,3,2]
// Output: -1
// Explanation:
// There is no i and j such that i < j and nums[i] < nums[j].

// Example 3:
// Input: nums = [1,5,2,10]
// Output: 9
// Explanation:
// The maximum difference occurs with i = 0 and j = 3, nums[j] - nums[i] = 10 - 1 = 9.

// Constraints:
//     n == nums.length
//     2 <= n <= 1000
//     1 <= nums[i] <= 10^9

import "fmt"

func maximumDifference(nums []int) int {
    res, mn:= -1, nums[0]
    for i := 1; i < len(nums); i++ {
        if nums[i] < mn {
            mn = nums[i]
        } else {
            diff := nums[i] - mn
            if diff > res{
                res = diff
            }
        }
    }
    if res <= 0 { return -1 }
    return res
}

func main() {
    // Example 1:
    // Input: nums = [7,1,5,4]
    // Output: 4
    // Explanation:
    // The maximum difference occurs with i = 1 and j = 2, nums[j] - nums[i] = 5 - 1 = 4.
    // Note that with i = 1 and j = 0, the difference nums[j] - nums[i] = 7 - 1 = 6, but i > j, so it is not valid.
    fmt.Println(maximumDifference([]int{7,1,5,4})) // 4
    // Example 2:
    // Input: nums = [9,4,3,2]
    // Output: -1
    // Explanation:
    // There is no i and j such that i < j and nums[i] < nums[j].
    fmt.Println(maximumDifference([]int{9,4,3,2})) // -1
    // Example 3:
    // Input: nums = [1,5,2,10]
    // Output: 9
    // Explanation:
    // The maximum difference occurs with i = 0 and j = 3, nums[j] - nums[i] = 10 - 1 = 9.
    fmt.Println(maximumDifference([]int{1,5,2,10})) // 9

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