开散列。当产生重复映射时，在这个位置维护一个链表来记录这些值。

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<double, double> pdd;

const int N = 20000;
const int HASH = 13331;

struct P
{
    int val;
    int cnt = 0;
    P* ne;
    P(int val, P* ne):val(val), ne(ne){}
};

P* head[N];

bool cmp(pii a, pii b){
    return a.first < b.first;
}

void init(){
    for(int i = 0; i < N; i++) head[i] = nullptr;
}

int H(int x){
    return (x % HASH) + 1;
}

void insert(int x){
    P* cur = head[H(x)];
    bool fg = true;
    while(cur != nullptr){
        if(cur->val == x){
            fg = false;
            break;
        }
        cur = cur->ne;
    }
    if(fg){
        cur = new P(x, head[H(x)]);
        head[H(x)] = cur;
    }
    cur->cnt++;
}

int main(){
    init();
    int n;
    cin >> n;
    for(int i = 0; i < n; i++){
        int x;
        cin >> x;
        insert(x);
    }

    vector<pii>res;
    for(int i = 0; i <= HASH + 1; i++){
        P* cur = head[i];
        while(cur != nullptr){
            res.push_back({cur->val, cur->cnt});
            cur = cur->ne;
        }
    }

    sort(res.begin(), res.end(), cmp);
    for(auto it : res){
        cout << it.first << ' ' << it.second<<endl;
    }
}