UVa-11991 https://uva.onlinejudge.org/external/119/p11991.pdf

11991.cpp

#include <iostream>
#include <vector>
#include <cstring>

int main()
{
    using namespace std;
    
    while (true) {
        int n, m;
        cin >> n >> m;
        if (cin.eof())
            break;
            
        static int vtable[1000000];
        int vcount = 0;
        vector< vector<int> > occurence;
        
        memset(vtable, 0, sizeof (vtable));
        
        int i = 0;
        while (n--) {
            int u;
            cin >> u;
            --u;
            
            if (vtable[u] == 0) {
                vtable[u] = ++vcount;
                occurence.push_back({++i});
            }
            else
                occurence[vtable[u] - 1].push_back(++i);
        }

        while (m--) {
            unsigned int k, v;
            cin >> k >> v;
            --k;
            --v;
            
            if (vtable[v] == 0 || occurence[vtable[v] - 1].size() <= k)
                cout << '0' << endl;
            else
                cout << occurence[vtable[v] - 1][k] << endl;
        }
    }
    
    return 0;
}