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Print all repeating adjacent pairs in sorted order from an array
  • Last Updated : 01 Feb, 2021

Given an array arr[] consisting of N integers, the task is to print all adjacent integer pairs from the array which appears more than once in the given array. If the array contains more than one such pair, print all pairs in sorted order.

Examples:

Input: arr[] = {1, 2, 5, 1, 2}
Output:
1 2
Explanation:
1 2 is the only repeating integer pair in the array.

Input: arr[] = {1, 2, 3, 4, 1, 2, 3, 4, 1, 2}
Output:
1 2
2 3
3 4
4 1
Explanation:
Since the array has more than one repeating pair, all the pairs are printed in the sorted order.

Approach: The simplest approach is to traverse the array and store every adjacent pair in a Map. Print all such pairs having frequency greater than 1. Follow the steps below to solve the problem:



  1. Create a Map M to store all adjacent pairs in an array.
  2. Traverse the given array and store every adjacent pair in the Map M.
  3. After the above step, traverse the map, and if the frequency of any pair is at least one, then insert it into a vector V.
  4. Sort the vector v in ascending order and print all the pairs stored in it.

Below is the implementation of the above approach:

C++




// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to print adjacent pairs
// in sorted order
void repeated_pairs(int arr[], int N)
{
    // Store the frequency of all
    // the adjacent pairs
    map<pair<int, int>, int> m;
 
    // Stores the resultant pairs
    vector<pair<int, int> > v;
    int i, j;
 
    // Stores the count of all
    // adjacent pairs
    for (i = 0; i < N - 1; i++) {
 
        pair<int, int> p
            = { arr[i], arr[i + 1] };
 
        // Increment the count of pair
        m[p]++;
    }
 
    // Store pairs that appears more
    // than once
    for (auto i = m.begin();
         i != m.end(); i++) {
 
        // If frequency is at least 1
        if (i->second > 1) {
            pair<int, int> p = i->first;
 
            // Insert pair into vector
            v.push_back(p);
        }
    }
 
    // Sort the vector
    sort(v.begin(), v.end());
 
    // Print the pairs
    for (i = 0; i < v.size(); i++) {
 
        pair<int, int> p = v[i];
 
        // Print the pair
        cout << p.first << " "
             << p.second << endl;
    }
}
 
// Driver Code
int main()
{
    // Given arr[]
    int arr[] = { 1, 2, 3, 4, 1,
                  2, 3, 4, 1, 2 };
 
    int N = sizeof(arr) / sizeof(arr[0]);
 
    // Function call
    repeated_pairs(arr, N);
 
    return 0;
}

Java




// Java code of above approach
import java.util.*;
import java.lang.*;
 
class pair
{
  int first, second;   
  pair(int f, int s)
  {
    this.first = f;
    this.second = s;
  }
 
  @Override
  public boolean equals(Object obj)
  {
 
    // if both the object references are 
    // referring to the same object.
    if(this == obj)
      return true;
 
    if(obj == null || obj.getClass() != this.getClass())
      return false;
 
    // type casting of the argument. 
    pair p = (pair) obj;
 
    return (p.first == this.first  && p.second == this.second);
  }
  @Override
  public int hashCode()
  {
    return this.first + this.second/2;
  }
}
class GFG {
 
  // Function to print adjacent pairs
  // in sorted order
  static void repeated_pairs(int arr[], int N)
  {
 
    // Store the frequency of all
    // the adjacent pairs
    Map<pair, Integer> m=new HashMap<>();
 
    // Stores the resultant pairs
    ArrayList<pair> v = new ArrayList<>();
    int i, j;
 
    // Stores the count of all
    // adjacent pairs
    for (i = 0; i < N - 1; i++)
    {
 
      pair p = new pair(arr[i], arr[i + 1]);
 
      // Increment the count of pair
      m.put(p,m.getOrDefault(p, 0) + 1);
 
    }
 
    // Store pairs that appears more
    // than once
    for (Map.Entry<pair,Integer> k: m.entrySet())
    {
 
      // If frequency is at least
      if (k.getValue() > 1)
      {
 
        // Insert pair into vector
        v.add(k.getKey());
      }
    }
 
    // Sort the vector
    Collections.sort(v, (a, b)->a.first-b.first);
 
    // Print the pairs
    for (pair k:v)
    {
 
      // Print the pair
      System.out.println(k.first + " " + k.second);
    }
  }  
 
  // Driver code
  public static void main(String[] args)
  {
 
    // Given arr[]
    int arr[] = { 1, 2, 3, 4, 1,
                 2, 3, 4, 1, 2 };
 
    int N = arr.length;
 
    // Function call
    repeated_pairs(arr, N);
  }
}
 
// This code is contributed by offbeat

Python3




# Python3 program for the above approach
 
# Function to print adjacent pairs
# in sorted order
def repeated_pairs(arr, N):
     
    # Store the frequency of all
    # the adjacent pairs
    m = {}
 
    # Stores the resultant pairs
    v = []
 
    # Stores the count of all
    # adjacent pairs
    for i in range(N - 1):
        p = (arr[i], arr[i + 1])
 
        # Increment the count of pair
        m[p] = m.get(p, 0) + 1
 
    # Store pairs that appears more
    # than once
    for i in m:
         
        # If frequency is at least 1
        if (m[i] > 1):
            p = i
             
            # Insert pair into vector
            v.append(p)
 
    # Sort the vector
    v = sorted(v)
 
    # Print the pairs
    for i in range(len(v)):
        p = v[i]
 
        # Print the pair
        print(p[0], p[1])
 
# Driver Code
if __name__ == '__main__':
     
    # Given arr[]
    arr = [ 1, 2, 3, 4, 1,
            2, 3, 4, 1, 2 ]
 
    N = len(arr)
 
    # Function call
    repeated_pairs(arr, N)
 
# This code is contributed by mohit kumar 29
Output: 
1 2
2 3
3 4
4 1

 

Time Complexity: O(N*log N)
Auxiliary Space: O(N)

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