Find_duplicates_in_an_array.cpp

/*
Problem Statement:
------------------
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 -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. 
*/

// Link --> https://practice.geeksforgeeks.org/problems/find-duplicates-in-an-array/1

// Code:
class Solution
{
  public:
    vector <int> ans;
    vector<int> duplicates(int a[] , int n) 
    {
        ans.clear();
        
        bool flag = false;
        int temp[n] = {0};
        
        for(int i=0 ; i<n ; i++)
            temp[a[i]]++;
        
        for(int i=0 ; i<n ; i++)
        {
            if(temp[i] > 1)
            {
                flag = true;
                ans.push_back(i);
            }
        }
        
        if(flag)
            return ans;
        else
        {
            ans.push_back(-1);
            return ans;
        }
    }
};