# 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 ` `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); ` `    ``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 m = ``new` `HashMap(); ` `      `  `        ``// 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 `

## Python3

 `# Python program to check if we can make ` `# neighbors distinct. ` `def` `distantAdjacentElement(a, n): ` ` `  `    ``# dict used to count the frequency ` `    ``# of each element occuring in the ` `    ``# array ` `    ``m ``=` `dict``() ` ` `  `    ``# In this loop we count the frequency ` `    ``# of element through map m ` `    ``for` `i ``in` `range``(n): ` `        ``if` `a[i] ``in` `m: ` `            ``m[a[i]] ``+``=` `1` `        ``else``: ` `            ``m[a[i]] ``=` `1` ` `  `    ``# mx store the frequency of element which ` `    ``# occurs most in array . ` `    ``mx ``=` `0` ` `  `    ``# In this loop we calculate the maximum ` `    ``# frequency and store it in variable mx. ` `    ``for` `i ``in` `range``(n): ` `        ``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``: ` `        ``print``(``"NO"``) ` `    ``else``: ` `        ``print``(``"YES"``) ` ` `  ` `  `# Driver Code ` `if` `__name__ ``=``=` `"__main__"``: ` `    ``a ``=` `[``7``, ``7``, ``7``, ``7``] ` `    ``n ``=` `len``(a) ` `    ``distantAdjacentElement(a, n) ` ` `  `# This code is contributed by ` `# sanjeev2552 `

## 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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