백준 1940번: 주몽

문제출처: https://www.acmicpc.net/problem/1940

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.StringTokenizer;
 
public class Main {
    
    public static void main(String[] args) throws NumberFormatException, IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int N = Integer.parseInt(reader.readLine());
        int M = Integer.parseInt(reader.readLine());
        int count = 0;
        
        ArrayList<String> list = new ArrayList<>();
        StringTokenizer tokenizer = new StringTokenizer(reader.readLine());
        for(int i=0 ; i<N ; i++)
            list.add(tokenizer.nextToken());
 
        while(list.size() > 1){
            int value1 = Integer.parseInt(list.get(0));
            int value2 = M - value1;
            if(list.contains(String.valueOf(value2)) && value1!=value2){
                count++;
                list.remove(String.valueOf(value2));
            }
            list.remove(0);
        }
        
        System.out.println(count);
    }
}