알고리즘 & 자료구조/백준
백준 1253
by 신재권
2022. 9. 12.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.StringTokenizer;
class Main {
static int N;
static int[] A;
public static void main(String[] args) throws Exception {
input();
go();
}
private static boolean check(int target_idx) {
int L = 1, R = N;
int target = A[target_idx];
while (L < R) {
if (L == target_idx)
L++;
else if (R == target_idx)
R--;
else {
if (A[L] + A[R] > target)
R--;
else if (A[L] + A[R] == target)
return true;
else
L++;
}
}
return false;
}
private static void go() {
int ans = 0;
for (int i = 1; i <= N; i++) {
if (check(i))
ans++;
}
System.out.println(ans);
}
private static void input() throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st;
N = Integer.parseInt(br.readLine());
A = new int[N + 1];
st = new StringTokenizer(br.readLine());
for (int i = 1; i <= N; i++) {
A[i] = Integer.parseInt(st.nextToken());
}
Arrays.sort(A, 1, N + 1);
}
}