I took a pretty similar approach. But I am getting runtime error SIGABRT. Why is this so? Can anyone explain? Here is my code:

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
    int n1,n2,n3,n,x,c=0,l,z;
    cin>>n1>>n2>>n3;
    n=n1+n2+n3;
    vector<int> v,f;
   for(int i=0;i<n;i++){
        cin>>x;
        v.push_back(x);
    }
    sort(v.begin(),v.end());
    for(int i=0;i<n-1;i++){
 
    l=v.at(i);
    z=v.at(i+1);
    if((l==z)&&(l>c)){

Oh my mistake, I didnt notice that, thank you :)

Where can we find the intuitive algorithm tutorials that was mentioned for each question?