Sorting array and saving the old index in C++ - c++

Question

I am doing online challenge which has to do the following.
There is a contest going in a village. So in the first line input two numbers N (which is how many people will join the contest) and K (how many of them can go to stage 2).
After that, we input N times the votes for each candidate in both stages.
Example input:
5 3
9 2
3 10
5 6
8 4
6 5
As you can see, we input N=5, K=3, which means 5 candidates, so 5 additional lines and 3 of them which go to stage 2.
After we sort the array the candidates with most votes are the ones with 6, 8 and 9. So they're going to stage 2. The winner is the one who has most votes in the stage 2 of them. In this case, 6 has 5 votes which is the most (8 has 4 and 9 has 2) and therefore we output the index of the 6 which is 5.
What I got so far:
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
int arr[50],nizabackup[50],n,k,niza2[50],saveindex[50],indexp=0;
cin >> n >> k;
for(int i=0;i<n;i++)
{
cin >> arr[i] >> niza2[i];
nizabackup[i] = arr[i];
}
sort(arr,arr+n);
for(int j=n;j>=k;j--)
{
for(int k=0;k<n;k++)
{
if(arr[j]==nizabackup[k])
{
saveindex[0]=k;
indexp++;
}
}
}
sort(saveindex,saveindex+indexp);
cout << saveindex[indexp];
return 0;
}
I need a hint what to do and also additional question -- why my debugger doesn't read the second for loop?

Answer 1

OK, alternative implementation. There's more set-up, but read main first and see how much simpler the actual logic is.
#include <vector>
#include <iostream>
#include <algorithm>
struct Contestant {
int index;
int firstVote;
int secondVote;
Contestant(int i, int v1, int v2) : index(i), firstVote(v1), secondVote(v2)
{}
};
// return true if l should come before r in sorted result
bool byFirstVote(Contestant const &l, Contestant const &r) {
return l.firstVote > r.firstVote; // sort by first vote
}
bool bySecondVote(Contestant const &l, Contestant const &r) {
return l.secondVote > r.secondVote; // sort by second vote
}
int main()
{
int n, k;
std::cin >> n >> k;
// populate a single vector of {index, firstVote, secondVote}
std::vector<Contestant> contestants;
for(int i=0; i<n; i++) {
int v1, v2;
std::cin >> v1 >> v2;
contestants.push_back(Contestant(i+1, v1, v2));
}
// sort all by firstVote, then sort first k by secondVote
std::sort(contestants.begin(), contestants.end(), byFirstVote);
std::sort(contestants.begin(), contestants.begin()+k, bySecondVote);
std::cout << contestants.front().index << std::endl;
}
I'm storing the index (starting from 1, not zero, as per your example), and both votes, all together in a single structure.
Then, I just change which field I sort on.