Find duplicates in an array solution in cpp

 

Given an array a[] of size N which contains elements from 0 to N-1, you need to find all the elements occurring more than once in the given array.

Example 1:

Input:
N = 4
a[] = {0,3,1,2}
Output: -1
Explanation: N=4 and all elements from 0
to (N-1 = 3) are present in the given
array. Therefore output is -1.

Example 2:

Input:
N = 5
a[] = {2,3,1,2,3}
Output: 2 3 
Explanation: 2 and 3 occur more than once
in the given array.

Your Task:
Complete the function duplicates() which takes array a[] and n as input as parameters and returns a list of elements that occur more than once in the given array in sorted manner. If no such element is found, return list containing [-1]. 

Expected Time Complexity: O(n).
Expected Auxiliary Space: O(n).
Note : The extra space is only for the array to be returned.
Try and perform all operation withing the provided array. 

Constraints:
1 <= N <= 105
0 <= A[i] <= N-1, for each valid i.

solution:

class Solution{
  public:
    vector<int> duplicates(int arr[], int n) {
        // code here
        vector<int> v;
        
        sort(arr,arr+n);
        
        for(int i=0;i<n;i++)
        {
            if(arr[i]==arr[i+1])
            {
                v.push_back(arr[i]);
            }
        }
        
        v.erase(unique(v.begin(),v.end()),v.end());
       
        if(v.empty())
        {
            v.push_back(-1);
        }
        
        return v;
    }
};