队列 + 字典

#include<iostream>
#include<algorithm>
#include<queue>
using namespace std;
queue<int> que;
const int N = 1005;
bool dict[N];
int main () {
    int m,n,cnt = 0;
    cin >> m >> n;
    for (int i = 1;i <= n;i++) {
        int x;
        cin >> x;
        if (!dict[x]) {
            cnt++;
            que.push(x);
            dict[x] = true;
            if (que.size() > m) {
                dict[que.front()] = false;
                que.pop();
            }
        }
    }
    cout << cnt << endl;
}