main.go

// Source: https://leetcode.com/problems/maximum-difference-between-increasing-elements
// Title: Maximum Difference Between Increasing Elements
// Difficulty: Easy
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 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`
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package main

func maximumDifference(nums []int) int {
	n := len(nums)

	ans := -1
	minNum := nums[0]
	for i := 1; i < n; i++ {
		num := nums[i]
		ans = max(ans, num-minNum)
		minNum = min(minNum, num)
	}

	if ans <= 0 {
		ans = -1
	}
	return ans
}