CODEKAT HUNTER SET1

q1.cpp

/** Coded By Xvamp999 **/

#include <bits/stdc++.h>

using namespace std;

unsigned long long mod=1000000007;

int main(){
 int n;
 cin>>n;

 set<string> reg_nos;
 string reg_no;

 set<string> dups;

 for(int i=0;i<n;i++){
    cin>>reg_no;

    // Convert registration number to lower case
    transform(reg_no.begin(),reg_no.end(),reg_no.begin(),::tolower);

    if(reg_nos.count(reg_no)!=0){
        dups.insert(reg_no);
    }else{
        reg_nos.insert(reg_no);
    }
 }

 for(auto itr=dups.begin();itr!=dups.end();itr++){
    cout<< *itr <<endl;
 }

 return 0;
}

q3.cpp

/** Coded By Xvamp999 **/

#include <bits/stdc++.h>

#define pb push_back
#define mp make_pair
#define fir first
#define sec second
#define pi acos(-1)
#define ll long long

using namespace std;

unsigned long long mod=1000000007;

int main(){

 int n;
 cin>>n;

 int arr[n];
 for(int i=0;i<n;i++)
    cin>>arr[i];

 // Question find "an" integer where arr[i]==i
 // Given array is sorted and distinct

 for(int i=0;i<n;i++){

    if(arr[i]<0) // i cant be -ve
        continue;

    else if(arr[i]==i){
        cout<<i;
        break;
    }
    else if(arr[i] > i ){   // if arr[i]>i  then there is no way that, the following numbers can hold the condition arr[i]==i
                            // as they are distinct and sorted
        cout<<"Nil"<<endl;
        break;

    }

 }

 return 0;
}

q4.cpp

/** Coded By Xvamp999 **/

#include <bits/stdc++.h>

#define pb push_back
#define mp make_pair
#define fir first
#define sec second
#define pi acos(-1)
#define ll long long

using namespace std;

unsigned long long mod=1000000007;

int main(){

 int n;
 cin>>n;

 int arr[n];
 for(int i=0;i<n;i++)
    cin>>arr[i];

 //Using property of XOR's
 int ans=arr[0];
 for(int i=1;i<n;i++)
    ans= ans ^ arr[i];

 cout<<ans;

 return 0;
}

q6.cpp

/** Coded By Xvamp999 **/

#include <bits/stdc++.h>

#define pb push_back
#define mp make_pair
#define fir first
#define sec second
#define pi acos(-1)
#define ll long long

using namespace std;

unsigned long long mod=1000000007;

int main(){

 int n;
 cin>>n;

 int arr[n];
 set<int> set1;

 bool flag=false;
 int ans;
 for(int i=0;i<n;i++){
    cin>>arr[i];
    if(set1.count(arr[i]) == 0 )
        set1.insert(arr[i]);
    else if(flag==false && set1.count(arr[i]) !=0 ){
        flag=true;
        ans=arr[i];
    }
 }

 cout<<ans;

 return 0;
}