题解（map + set）

#include <set>
#include <map>
#include <iostream>
#include <algorithm>
#include <utility>
using namespace std;

set <int> st;
map <int, int> mp;

int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int x;
        cin >> x;
        if (st.count(x)) {
            mp[x]++;
        } else {
            mp[x] = 1;
            st.insert(x);
        }
    }
    for (auto i : st) cout << i << " " << mp[i] << endl;
    return 0;
}