Distinct adjacent elements in an array

Given an array, find whether it is possible to obtain an array having distinct neighbouring elements by swapping two neighbouring array elements.

Examples:

Input : 1 1 2
Output : YES
swap 1 (second last element) and 2 (last element), 
to obtain 1 2 1, which has distinct neighbouring 
elements .

Input : 7 7 7 7
Output : NO
We can't swap to obtain distinct elements in 
neighbor .

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

To obtain an array having distinct neighbouring elements is possible only, when the frequency of most occurring element is less than or equal to half of size of array i.e ( <= (n+1)/2 ). To make it more clear consider different examples

1st Example : a[] = {1, 1, 2, 3, 1}
We can obtain array {1, 2, 1, 3, 1} by
swapping (2nd and 3rd) element and
(4th and 5th) elements from array a.
Here 1 occurs most and its frequency is
3 (6+1)/2.
Hence, it will never possible.

Below is the implementation of this approach .

C++

// C++ program to check if we can make 
// neighbors distinct. 
#include <bits/stdc++.h> 
using namespace std; 
  
void distinctAdjacentElement(int a[], int n) 
{ 
    // map used to count the frequency 
    // of each element occuring in the 
    // array 
    map<int, int> m; 
  
    // In this loop we count the frequency 
    // of element through map m . 
    for (int i = 0; i < n; ++i) 
        m[a[i]]++; 
  
    // mx store the frequency of element which 
    // occurs most in array . 
    int mx = 0; 
  
    // In this loop we calculate the maximum 
    // frequency and store it in variable mx. 
    for (int i = 0; i < n; ++i) 
        if (mx < m[a[i]]) 
            mx = m[a[i]]; 
  
    // By swapping we can adjust array only 
    // when the frequency of the element 
    // which occurs most is less than or 
    // equal to (n + 1)/2 . 
    if (mx > (n + 1) / 2) 
        cout << "NO" << endl; 
    else
        cout << "YES" << endl; 
} 
  
// Driver program to test the above function 
int main() 
{ 
    int a[] = { 7, 7, 7, 7 }; 
    int n = sizeof(a) / sizeof(a[0]); 
    distinctAdjacentElement(a, n); 
    return 0; 
} 

Java

// Java program to check if we can make 
// neighbors distinct. 
import java.io.*; 
import java.util.HashMap; 
import java.util.Map; 
class GFG { 
      
    static void distinctAdjacentElement(int a[], int n) 
    { 
        // map used to count the frequency 
        // of each element occuring in the 
        // array 
        HashMap<Integer,Integer> m = new HashMap<Integer, 
                                             Integer>(); 
       
        // In this loop we count the frequency 
        // of element through map m . 
        for (int i = 0; i < n; ++i){ 
     
            // checks if map already contains a[i] then  
            // update the previous value by incrementing  
          // by 1 
            if(m.containsKey(a[i])){ 
                int x = m.get(a[i]) + 1; 
                m.put(a[i],x);  
            } 
            else{ 
                m.put(a[i],1); 
            } 
              
        } 
       
        // mx store the frequency of element which 
        // occurs most in array . 
        int mx = 0; 
       
        // In this loop we calculate the maximum 
        // frequency and store it in variable mx. 
        for (int i = 0; i < n; ++i) 
            if (mx < m.get(a[i])) 
                mx = m.get(a[i]); 
       
        // By swapping we can adjust array only 
        // when the frequency of the element 
        // which occurs most is less than or 
        // equal to (n + 1)/2 . 
        if (mx > (n + 1) / 2) 
            System.out.println("NO"); 
        else
            System.out.println("YES"); 
    } 
          
    // Driver program to test the above function 
    public static void main (String[] args) { 
        int a[] = { 7, 7, 7, 7 }; 
        int n = 4; 
        distinctAdjacentElement(a, n); 
    } 
} 
// This code is contributed by Amit Kumar 

C#

// C# program to check if we can make  
// neighbors distinct.  
using System; 
using System.Collections.Generic; 
  
class GFG { 
  
public static void distinctAdjacentElement(int[] a, int n) 
{ 
    // map used to count the frequency  
    // of each element occuring in the  
    // array  
    Dictionary<int, int> m = new Dictionary<int, int>(); 
  
    // In this loop we count the frequency  
    // of element through map m .  
    for (int i = 0; i < n; ++i) 
    { 
  
        // checks if map already  
        // contains a[i] then  
        // update the previous 
        // value by incrementing  
        // by 1  
        if (m.ContainsKey(a[i])) 
        { 
            int x = m[a[i]] + 1; 
            m[a[i]] = x; 
        } 
        else
        { 
            m[a[i]] = 1; 
        } 
  
    } 
  
    // mx store the frequency 
    // of element which  
    // occurs most in array .  
    int mx = 0; 
  
    // In this loop we calculate 
    // the maximum frequency and 
    // store it in variable mx.  
    for (int i = 0; i < n; ++i) 
    { 
        if (mx < m[a[i]]) 
        { 
            mx = m[a[i]]; 
        } 
    } 
  
    // By swapping we can adjust array only  
    // when the frequency of the element  
    // which occurs most is less than or  
    // equal to (n + 1)/2 .  
    if (mx > (n + 1) / 2) 
    { 
        Console.WriteLine("NO"); 
    } 
    else
    { 
        Console.WriteLine("YES"); 
    } 
} 
  
    // Main Method 
    public static void Main(string[] args) 
    { 
        int[] a = new int[] {7, 7, 7, 7}; 
        int n = 4; 
        distinctAdjacentElement(a, n); 
    } 
} 
  
// This code is contributed 
// by Shrikant13 

Output:

NO

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