Problem:
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Maximum Profit

You can obtain profits from foreign exchange margin transactions. For example, if you buy 1000 dollar at a rate of 100 yen per dollar, and sell them at a rate of 108 yen per dollar, you can obtain (108 - 100) × 1000 = 8000 yen.

Write a program which reads values of a currency $R_t$ at a certain time $t$ ($t = 0, 1, 2, ... n-1$), and reports the maximum value of $R_j - R_i$ where $j > i$ .

Input

The first line contains an integer $n$. In the following $n$ lines, $R_t$ ($t = 0, 1, 2, ... n-1$) are given in order.

Output

Print the maximum value in a line.

Constraints

$2 \leq n \leq 200,000$

$1 \leq R_t \leq 10^9$

Sample Input 1

6
5
3
1
3
4
3

Sample Output 1

3

Sample Input 2

3
4
3
2

Sample Output 2

-1

Solution in JAVA (judge verdict: Time Limit Exceeded)

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

class Main {
	private static Scanner scanner;
	public static void main(String[] args) {
		int answer = 0;
		int count = 0;
		boolean flag = false;
		List<Integer> list = new ArrayList<Integer>();
		scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		for(int i=0; i<n; i++){
			list.add(scanner.nextInt());
		}
		List<Integer> distinctList = distinct(list);
		Collections.sort(distinctList);
		if(distinctList.size() > 20){count = 20;}
		else{ count = distinctList.size();}
		for(int i=0; i<count; i++){
			int maxIndex = list.lastIndexOf(distinctList.get(distinctList.size() - (i + 1)));
			List<Integer> tmpList = list.subList(0, maxIndex);
			if((!tmpList.isEmpty())){
				if(!flag){
					answer = distinctList.get(distinctList.size() - (i+1)) - Collections.min(tmpList);
					flag = true;
				}
				else if(answer < (distinctList.get(distinctList.size() - (i+1)) - Collections.min(tmpList))){
					answer = distinctList.get(distinctList.size() - (i+1)) - Collections.min(tmpList);
				}
			}
		}
		System.out.println(answer);
	}
	public static List<Integer> distinct(List<Integer> list){
		List<Integer> distictList = new ArrayList<Integer>();
		for(int i: list){
			if(!distictList.contains(i))distictList.add(i);
		}
		return distictList;
	}
}