keeping track of vector pair indices upon sorting - c++

Question

Similar things have been asked before but I am having trouble applying the concept. I would like to to keep track of the indices of the pairs in my vector of pairs then, once sorted, std::cout the input order.
e.g.
cin >> 5 6 1 5 1 2 1 2 3 5
cout << 1 2 1 2 1 5 3 5 5 6
cout >> 3 4 2 5 1 //and this is where I am having trouble.
I was thinking of converting to triples, where one of the elements is the index but I couldn't get that to conform to my needs.
Any help would be appreciated. Thank you.
#include <iostream>
#include <cmath>
#include <vector>
#include <cstdlib>
using namespace std;
bool compare(const pair<int,int>&A, const pair<int,int>&B);
int main()
{
vector<pair<int,int>> v;
pair<int,int> tok;
while(cin >> tok.first>>tok.second){v.push_back(tok);}
sort(v.begin(),v.end(), compare);
for(int i = (signed int)v.size()-1; i >= 0 ; i--)
{
cout << v.at(i).first << " ";
cout << v.at(i).second << " ";
}
cout << endl;
return 0;
}
bool compare(const pair<int,int>&A, const pair<int,int>&B)
{
return A.first > B.first;
}

Answer 1

Here's one way to do it. Long time since I did someone's homework for them ;-)
#include <iostream>
#include <vector>
#include <sstream>
using namespace std;
const string input_data = "5 6 1 5 1 2 1 2 3 5";
typedef pair<int, int> integer_pair;
typedef pair<int, integer_pair> integer_pair_with_input_order;
bool less_by_integer_pair(const integer_pair_with_input_order& l,
const integer_pair_with_input_order& r)
{
return l.second < r.second;
}
int main()
{
// note - I did this to avoid having to type numbers in.
std::istringstream simulate_cin(input_data);
vector<integer_pair_with_input_order> v;
integer_pair tok;
int input_order = 0;
while(simulate_cin >> tok.first >> tok.second) {
v.push_back(make_pair(++input_order, tok));
}
sort(v.begin(),v.end(), less_by_integer_pair);
for (int i = 0 ; i < v.size() ; ++i)
{
const integer_pair_with_input_order& elem = v[i];
cout << "input order : " << elem.first
<< " { " << elem.second.first
<< ", " << elem.second.second << " }\n";
}
return 0;
}