백준 - 1940(주몽)

package algorithm_practical;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

public class algo_1940 {
	public static void main(String[] args) throws IOException {

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

		StringTokenizer st = new StringTokenizer(br.readLine());

		int N = Integer.parseInt(st.nextToken()); // 재료의 개수
		st = new StringTokenizer(br.readLine());
		int M = Integer.parseInt(st.nextToken()); // 타겟 넘버
		int[] J = new int[N];

		// 입력 배열 처리
		st = new StringTokenizer(br.readLine());
		for (int i = 0; i < N; i++) {
			J[i] = Integer.parseInt(st.nextToken());
		}

		Arrays.sort(J);

		int sum = 0;
		int count = 0;
		int start_index = 0;
		int end_index = J.length - 1;

//sum의 값이 타켓넘버가 될때까지 한다 
		while (start_index < end_index) {
			sum = J[start_index] + J[end_index];
			if (sum < M) {
				start_index++;
			} else if (sum > M) {
				end_index--;
			} else {
				start_index++;
				end_index--;
				count++;
			}

		}
		bw.write(String.valueOf(count));
		bw.newLine();
        bw.flush();
        br.close();
        bw.close();

	}

}