[백준] 1253번 좋다

#include <iostream>
#include <vector>
#include <algorithm>
#define fastio cin.tie(0)->sync_with_stdio(0)
using namespace std;

int main() {
    fastio;
    int N, count = 0;
    cin >> N;

    vector<int> col(N);
    for (int i = 0; i < N; i++) {
        cin >> col[i];
    }
    sort(col.begin(), col.end()); 

    for (int i = 0; i < N; i++) {
        int val = col[i]; // 현재 확인할 값
        int l = 0, r = N - 1;

        while (l < r) {
            if (l == i) {
                l++;
                continue;
            }
            if (r == i) {
                r--;
                continue;
            }
            int sum = col[l] + col[r];
            if (sum == val) {
                count++; 
                break;
            } 
            else if (sum < val) {
                l++;
            } 
            else {
                r--;
            }
        }
    }
    cout << count << '\n'; 
    return 0;
}