Find duplicates in an array

Problem Statement - link #

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.

Note: The extra space is only for the array to be returned. Try and perform all operations within the provided 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 a sorted manner. If no such element is found, return list containing [-1].

Expected Time Complexity: O(N)
Expected Auxiliary Space: O(N)

Examples #

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.

Constraints #

• 1 <= N < 10^5
• 0 <= arr[i] < N-1

Solutions #

class Solution{
  public:
    vector<int> duplicates(int arr[], int n) {
        // code here
        vector<int> temp(n,0), res;
        for(int i = 0; i < n; i++) {
            temp[arr[i]]++;
        }
        for(int i = 0; i < n; i++) {
            if(temp[i] > 1) {
                res.push_back(i);
            }
        }
        if(res.size() == 0) {
            res.push_back(-1);
        }
        return res;
        
    }
};