Check if all duplicate elements in the Array are adjacent or not

Given an array arr[]. The task is to check whether duplicate elements in arr[] are contiguous or not. 

Examples:

Input: arr[] = {1, 2, 3, 4, 5, 6}
Output: Yes
Explanation: There is no duplicate element in arr[] so 
there is no need to check anything and answer is Yes. 

Input: arr[] = {1, 2, 2, 4}
Output: Yes
Explanation: 2 is occurring 2 times and it is contiguous. Hence, answer is Yes.

Input: arr[] = {1, 2, 3, 2, 4}
Output: No
Explanation: There is a gap between 2's and 3 is between two 2's. Therefore, the answer is No. 

Approach: 

This problem can be solved by using HashMaps. Follow the steps below to solve the given problem. 

• Use maps to store the visited elements.
• First, mark the first element on the map.
• Traverse the array arr[] from 1 to N-1. where N is the size of arr[].
• If the current element matches the previous element means there is a cycle of one element repeating so simply continue the loop.
• If the current element is already marked in the map return "No".
• Mark the current element in the map.
• If the function reaches here means there are all contiguous elements so return "Yes".

Below is the implementation of the above approach. 

// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;

// Function to check whether duplicate
// elements in array arr[] are contiguous or not
string checkContiguous(int* arr, int& n)
{
    int i;

    // Map to keep track of elements
    unordered_map<int, bool> visited;

    visited.clear();
    visited.insert({ arr[0], 1 });

    for (i = 1; i < n; i++) {
        if (arr[i] == arr[i - 1])
            continue;
        else if (visited[arr[i]])
            return "No";
        visited[arr[i]] = 1;
    }

    return "Yes";
}

// Driver Code
int main()
{
    int arr[] = { 2, 4, 5, 5, 3, 5 };
    int N = sizeof(arr) / sizeof(arr[0]);

    // Function Call
    cout << checkContiguous(arr, N);

    return 0;
}

// Java code for the above approach
import java.io.*;

class GFG {

  // Function to check whether duplicate
  // elements in array arr[] are contiguous or not
  static String checkContiguous(int[] arr, int n)
  {
    int i;

    // Map to keep track of elements
    int[] visited = new int[n];

    for (i = 1; i < n; i++) {
      if (arr[i] == arr[i - 1])
        continue;
      else if (visited[arr[i]] == 0)
        return "No";
      visited[arr[i]] = 1;
    }

    return "Yes";
  }

  // Driver Code
  public static void main(String[] args)
  {

    int arr[] = { 2, 4, 5, 5, 3, 5 };
    int N = arr.length;

    // Function Call
    System.out.println(checkContiguous(arr, N));
  }
}

// This code is contributed by Potta Lokesh

# Python program for the above approach

# Function to check whether duplicate
# elements in array arr[] are contiguous or not
def checkContiguous  (arr, n):
    i = None

    # Map to keep track of elements
    visited = [0] * n;


    for i in range(1, n):
        if (arr[i] == arr[i - 1]):
            continue;
        elif (visited[arr[i]] == 0):
            return "No";
        visited[arr[i]] = 1;
    

    return "Yes";


# Driver Code

arr = [2, 4, 5, 5, 3, 5];
N = len(arr)

# Function Call
print(checkContiguous(arr, N));

# This code is contributed by Saurabh Jaiswal

// C# code for the above approach
using System;
class GFG {

  // Function to check whether duplicate
  // elements in array arr[] are contiguous or not
  static String checkContiguous(int[] arr, int n)
  {
    int i;

    // Map to keep track of elements
    int[] visited = new int[n];

    for (i = 1; i < n; i++) {
      if (arr[i] == arr[i - 1])
        continue;
      else if (visited[arr[i]] == 0)
        return "No";
      visited[arr[i]] = 1;
    }

    return "Yes";
  }

  // Driver Code
  public static void Main()
  {

    int[] arr = { 2, 4, 5, 5, 3, 5 };
    int N = arr.Length;

    // Function Call
    Console.WriteLine(checkContiguous(arr, N));
  }
}

// This code is contributed by ukasp.

<script>
    // JavaScript program for the above approach

    // Function to check whether duplicate
    // elements in array arr[] are contiguous or not
    const checkContiguous = (arr, n) => {
        let i;

        // Map to keep track of elements
        let visited = {};

        visited[arr[0]] = 1;

        for (i = 1; i < n; i++) {
            if (arr[i] == arr[i - 1])
                continue;
            else if (visited[arr[i]])
                return "No";
            visited[arr[i]] = 1;
        }

        return "Yes";
    }

    // Driver Code

    let arr = [2, 4, 5, 5, 3, 5];
    let N = arr.length;

    // Function Call
    document.write(checkContiguous(arr, N));

// This code is contributed by rakeshsahni

</script>

No

Time Complexity: O(N) // only one traversal of the array is required

Auxiliary Space: O(N) //unordered map takes space equal to the length of the array N