백준 3273번 두 수의 합 C++

출처 : https://www.acmicpc.net/problem/3273

 

#include <iostream>
#include <string>
#include <vector>
#include <math.h>
#include <algorithm>
#include <utility>
#include <stack>
#include <queue>
#include <math.h>
#include <set>
#include <map>
#include <list>
#include <unordered_map>
#include <unordered_set>
#include <iomanip>
#include <limits.h>

#include <bitset>

using namespace std;
using int64 = long long;

int n, x;
vector<int> v;

unordered_set<int> s;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
	cout.tie(NULL);

    cin >> n;
    v = vector<int>(n);
    for (int i = 0; i < n; i++) {
        cin >> v[i];
        s.insert(v[i]);
    }
    cin >> x;

    int cnt = 0;

    for (int i = 0; i < n; i++) {
        int target = x - v[i];
        if (target == v[i]) continue;
        if (target <= 0) continue;
        auto it = s.find(target);
        if (it == s.end()) continue;
        cnt++;

        s.erase(v[i]);
    }

    cout << cnt;
}