Check if a given array contains duplicate elements within k distance from each in C++

Here we will see how to check whether an unsorted array has duplicate elements within k distance from each other or not. Suppose a list of elements is {1, 2, 3, 1, 4, 5}, here if k = 3, then the program will return true, as the distance between two 1s is 3.

We will solve this using a hash table. The steps will be like below −

• Create one empty hash table
• For each index i, let the element e = arr[i] in the list, do
  • if e is present in the hash table, then return true
  • otherwise, add e to hash table, and remove (i-k)th element from the hash table if it exists, when i >= K.

Example

#include<iostream>
#include<set>
using namespace std;
bool hasDuplicateWithDistK(int arr[], int n, int k) {
   set<int> element_set;
   for (int i = 0; i < n; i++) {
      if (element_set.find(arr[i]) != element_set.end())
         return true;
      element_set.insert(arr[i]);
      if (i >= k)
         element_set.erase(arr[i-k]);
   }
   return false;
}
int main () {
   int arr[] = {10, 5, 3, 4, 3, 5, 6};
   int n = sizeof(arr) / sizeof(arr[0]);
   if (hasDuplicateWithDistK(arr, n, 3))
      cout << "Duplicate element has found";
   else
      cout << "Duplicate element has not found";
}

Output

Duplicate element has found