[SWEA][D2] 1859. 백만 장자 프로젝트 Java

import java.util.Scanner;  
  
class Solution  
{  
    public static void main(String args[]) throws Exception  
    {  
  
        Scanner sc = new Scanner(System.in);  
        int T;  
        T=sc.nextInt();  
  
  
        for(int test_case = 1; test_case <= T; test_case++)  
        {  
            int N = sc.nextInt();  
            int[] values = new int[N];  
  
            long profit = 0;  
            int maxPrice = 0;  
  
            for (int i = 0; i < N; i++) {  
                values[i] = sc.nextInt();  
            }  
  
            for (int i = N -1; i >= 0 ; i--) {  
                if(maxPrice < values[i]){  
                    maxPrice = values[i];  
                }else{  
                    profit = profit + (maxPrice - values[i]);  
                }  
            }  
  
            System.out.println("#" + test_case+ " "+profit);  
  
        }  
    }  
}

 

1. 자료형을 생각할것! long을 쓸수도있음
2. 거꾸로 계산하는 방법으로 문제를 풀수 있다는 사실을 생각할것