findMissingAndRepeatingElement.cpp

/* Given an unsorted array Arr of size N of positive integers. 
One number 'A' from set {1, 2, …N} is missing and one number 'B' occurs twice in array. 
Find these two numbers. */
#include <bits/stdc++.h>

using namespace std;

 // } Driver Code Ends
class Solution{
public:
    int *findTwoElement(int *arr, int n)
    {
       int c,i=1;
       int *a=new int[2];
       //iterating form i=0 to N
       while(i<=n)
       {
           //c-count occurance of i in array
           c=0;
           for(int j=0;j<n;j++)
           {
             //when i element is found in array then increase its occurance
               if(arr[j]==i)
                    c++;
           }
           //if i occur 2 times then its duplicat elements
           if(c==2)
                a[0]=i;
           //if i isnt found the its missing element
            else if(c==0)
                a[1]=i;
     
             i++;
       }
       return a;
    }

};

int main() {
        //n-array size
        int n;
        cin >> n;
        int a[n];
        for (int i = 0; i < n; i++)
            cin >> a[i];
        
        Solution ob;
        auto ans = ob.findTwoElement(a, n);
        cout << ans[0] << " " << ans[1] << "\n";
 
        return 0;
}