BOJ3273.java

package main.week4.BOJ3273;

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

/**
 * 두 수의 합
 * 정렬, 투 포인터
 * @author hazel
 */
public class BOJ3273 {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        int[] arr = new int[n];

        StringTokenizer st = new StringTokenizer(br.readLine());
        for (int i = 0; i < n; i++) {
            arr[i] = Integer.parseInt(st.nextToken());
        }
        int k = Integer.parseInt(br.readLine());

        //정렬
        Arrays.sort(arr);

        int cnt = 0;
        int left = 0;
        int right = n - 1;
        while (left < right) {
            int sum = arr[left] + arr[right];
            if (sum == k) {
                cnt++;
                left++;
                right--;
            } else if (sum > k) {
                right--;
            } else {
                left++;
            }
        }
        System.out.println(cnt);
    }
}