백준 알고리즘 4158번 : CD

링크

https://www.acmicpc.net/problem/4158

sol1) unordered_set

#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
#define X first
#define Y second
#define pb push_back
#define fastio cin.tie(0)->sync_with_stdio(0)
#define sz(v) (int)(v).size()
#define all(v) v.begin(), v.end()
#define rall(v) (v).rbegin(), (v).rend()
#define compress(v) sort(all(v)), (v).erase(unique(all(v)), (v).end())
#define OOB(x, y) ((x) < 0 || (x) >= n || (y) < 0 || (y) >= m)
#define debug(x) cout << (#x) << ": " << (x) << '\n'
using namespace std;
using ll = long long;
using ull = unsigned long long;
using dbl = double;
using ldb = long double;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using vi = vector<int>;
using vs = vector<string>;
using tii = tuple<int,int,int>;
template<typename T> using wector = vector<vector<T>>;

const int MOD = 1e9 + 7;
const int INF = 1e9 + 7;
const ll LNF = 1e18 + 7;

int main() {
  fastio;
  int n,m;
  while(cin >> n >> m && n != 0){
    unordered_set<int> S;
    for(int i = 0; i < n; i++){
      int a; cin >> a;
      S.insert(a);
    }
    int cnt = 0;
    for(int i = 0; i < m; i++){
      int x; cin >> x;
      if(S.count(x)) cnt++;
    }
    cout << cnt << "\n";
  }
  return 0;
}

sol2) 이분 탐색

#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
#define X first
#define Y second
#define pb push_back
#define fastio cin.tie(0)->sync_with_stdio(0)
#define sz(v) (int)(v).size()
#define all(v) v.begin(), v.end()
#define rall(v) (v).rbegin(), (v).rend()
#define compress(v) sort(all(v)), (v).erase(unique(all(v)), (v).end())
#define OOB(x, y) ((x) < 0 || (x) >= n || (y) < 0 || (y) >= m)
#define debug(x) cout << (#x) << ": " << (x) << '\n'
using namespace std;
using ll = long long;
using ull = unsigned long long;
using dbl = double;
using ldb = long double;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using vi = vector<int>;
using vs = vector<string>;
using tii = tuple<int,int,int>;
template<typename T> using wector = vector<vector<T>>;

const int MOD = 1e9 + 7;
const int INF = 1e9 + 7;
const ll LNF = 1e18 + 7;

int main() {
  fastio;
  int n,m;
  while(cin >> n >> m && n != 0){
    vi v;
    for(int i = 0; i < n; i++){
      int a; cin >> a;
      v.pb(a);
    }
    int cnt = 0;
    for(int i = 0; i < m; i++){
      int x; cin >> x;
      if(binary_search(all(v),x)) cnt++;
    }
    cout << cnt << "\n";
  }
  return 0;
}

set을 쓰면 시간초과가 나서 빌면서 unordered_set을 사용했습니다.
이분탐색으로도 가능하네요.