[백준 3273] 두 수의 합 (Java / Python)

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

public class Main{
    static int[] arr;
    
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int n = Integer.parseInt(br.readLine());
        arr = new int[n];
        
        StringTokenizer st = new StringTokenizer(br.readLine(), " ");
        for(int i=0; i<n; i++){
            arr[i] = Integer.parseInt(st.nextToken());
        }
    
        int x = Integer.parseInt(br.readLine());
    
        // 정렬하고
        Arrays.sort(arr);

        int ans=0, i=0, j=n-1;

        // 양 끝에서부터 
        while(true){
            if(i==j || i>j || j<i) break;

            if(arr[i]+arr[j]==x){
                ans++;
                i++; j--;
                continue;
            } else if(arr[i]+arr[j]>x){
                j--; 
                continue;
            } else {
                i++;
                continue;
            }
        }


        System.out.println(ans);
    }
}

정렬 구현해도 되고 Arrays.sort 써도 된다.
양 끝에서부터 비교하는게 핵심

 

+ python

import sys

read = sys.stdin.readline

n = int(read().rstrip())
arr = list(map(int, read().rstrip().split(" ")))
x = int(read().rstrip())

arr.sort()
start = 0
end = n-1
ans = 0

while start < end:
    if arr[start] + arr[end] == x:
        ans += 1
        start += 1
        end -= 1
    elif arr[start] + arr[end] < x:
        start += 1
    else:
        end -= 1


print(ans)