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# Maximise the size of consecutive element subsets in an array

• Difficulty Level : Hard
• Last Updated : 05 May, 2021

Given an integer array and an integer k. The array elements denote positions of points on a 1-D number line, find the maximum size of the subset of points that can have consecutive values of points which can be formed by placing another k points on the number line. Note that all coordinates should be distinct and elements of the array are in increasing order.

Examples:

```Input : arr[] = {1, 2, 3, 4, 10, 11, 14, 15},
k = 4
Output : 8
For maximum size subset, it is optimal to
choose the points on number line at
coordinates 12, 13, 16 and 17, so that the
size of the consecutive valued subset will
become 8 which will be maximum .

Input : arr[] = {7, 8, 12, 13, 15, 18}
k = 5
Output : 10
For maximum size subset, it is optimal to choose
the points on number line at coordinates 9, 10,
11, 14 and 16, so that the size of the consecutive
valued subset will become 10 which will be maximum .```

Brute force Approach ( Time Complexity – O(N2) ):

A brute force consists of checking all the possible (l, r) pairs for the condition ((arr[r]-arr[l])-(r-l)) ≤ k. In order to find out if a pair (l, r) is valid, we should check if the number of points that need to be placed between these two initial ones is not greater than K. Since arr[i] is the coordinate of the i-th point in the input array (arr), then we need to check if (arr[r] – arr[l]) – (r – l ) ≤ k.

This solution has a complexity of O(N2).

## C++

 `/* C++ program to find the maximum size of subset of``   ``points that can have consecutive values using``   ``brute force */``#include ``using` `namespace` `std;` `int` `maximiseSubset(``int` `arr[], ``int` `n, ``int` `k)``{``    ``// Since we can always enforce the solution``    ``// to contain all the K added points``    ``int` `ans = k;` `    ``for` `(``int` `l = 0; l < n - 1; l++)``        ``for` `(``int` `r = l; r < n; r++)` `            ``// check if the number of points that``            ``// need to be placed between these two``            ``// initial ones is not greater than k``            ``if` `((arr[r] - arr[l]) - (r - l) <= k)``                ``ans = max(ans, r - l + k + 1);` `    ``return` `(ans);``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 1, 2, 3, 4, 10, 11, 14, 15 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``int` `k = 4;``    ``printf``(``"%dn"``, maximiseSubset(arr, n, k));``    ``return` `0;``}`

## Java

 `/* Java program to find the maximum size of subset of``points that can have consecutive values using``brute force */``import` `java.util.*;` `class` `GFG``{` `    ``static` `int` `maximiseSubset(``int``[] arr, ``int` `n, ``int` `k)``    ``{``        ``// Since we can always enforce the solution``        ``// to contain all the K added points``        ``int` `ans = k;` `        ``for` `(``int` `l = ``0``; l < n - ``1``; l++)``            ``for` `(``int` `r = l; r < n; r++)` `                ``// check if the number of points that``                ``// need to be placed between these two``                ``// initial ones is not greater than k``                ``if` `((arr[r] - arr[l]) - (r - l) <= k)``                    ``ans = Math.max(ans, r - l + k + ``1``);` `        ``return` `(ans);``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int``[] arr = { ``1``, ``2``, ``3``, ``4``, ``10``, ``11``, ``14``, ``15` `};``        ``int` `n = arr.length;``        ``int` `k = ``4``;``        ``System.out.println(maximiseSubset(arr, n, k)); ``    ``}``}``/* This code is contributed by Mr. Somesh Awasthi */`

## Python3

 `# Python3 program to find the maximum size``# of subset of points that can have consecutive``# values using brute force` `def` `maximiseSubset(arr , n, k):` `    ``# Since we can always enforce the solution``    ``# to contain all the K added points``    ``ans ``=` `k` `    ``for` `l ``in` `range``(n ``-` `1``):``        ``for` `r ``in` `range``(l, n):` `            ``# check if the number of points that``            ``# need to be placed between these two``            ``# initial ones is not greater than k``            ``if` `((arr[r] ``-` `arr[l]) ``-` `(r ``-` `l) <``=` `k) :``                ``ans ``=` `max``(ans, r ``-` `l ``+` `k ``+` `1``)` `    ``return` `(ans)` `# Driver code``if` `__name__ ``=``=` `"__main__"``:``    ` `    ``arr ``=` `[ ``1``, ``2``, ``3``, ``4``, ``10``, ``11``, ``14``, ``15` `]``    ``n ``=` `len``(arr)``    ``k ``=` `4``    ``print``(maximiseSubset(arr, n, k))` `# This code is contributed by ita_c`

## C#

 `/* C# program to find the``maximum size of subset of``points that can have``consecutive values using``brute force */``using` `System;` `class` `GFG``{` `    ``static` `int` `maximiseSubset(``int``[] arr,``                              ``int` `n, ``int` `k)``    ``{``        ``// Since we can always enforce``        ``// the solution to contain all``        ``// the K added points``        ``int` `ans = k;` `        ``for` `(``int` `l = 0; l < n - 1; l++)``            ``for` `(``int` `r = l; r < n; r++)` `                ``// check if the number of``                ``// points that need to be``                ``// placed between these``                ``// two initial ones is not``                ``// greater than k``                ``if` `((arr[r] - arr[l]) -``                              ``(r - l) <= k)``                    ``ans = Math.Max(ans, r - l +``                                        ``k + 1);` `        ``return` `(ans);``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int``[] arr = {1, 2, 3, 4,``                    ``10, 11, 14, 15};``        ``int` `n = arr.Length;``        ``int` `k = 4;``        ``Console.WriteLine(maximiseSubset(arr, n, k));``    ``}``}` `// This code is contributed by anuj_67.`

## PHP

 ``

## Javascript

 ``

Output:

`8`

Efficient Approach (Time complexity – O(N))

In order to optimize the brute force, notice that if r increases, then l also increases (or at least stays the same). We can maintain two indexes. Initialize l and r both as 0. Then we start incrementing r. As we do this, at each step we increment l until the condition used in the brute force approach becomes true. When r reaches the last index, we stop.

## C++

 `/* C++ program to find the maximum size of subset``   ``of points that can have consecutive values``   ``using efficient approach */``#include ``using` `namespace` `std;` `int` `maximiseSubset(``int` `arr[], ``int` `n, ``int` `k)``{``    ``// Since we can always enforce the``    ``// solution to contain all the K added``    ``// points``    ``int` `ans = k;` `    ``int` `l = 0, r = 0;``    ``while` `(r < n) {` `        ``// increment l until the number of points``        ``// that need to be placed between index l``        ``// and index r is not greater than k``        ``while` `((arr[r] - arr[l]) - (r - l) > k)``            ``l++;``        ` `        ``// update the solution as below``        ``ans = max(ans, r - l + k + 1);``        ` `        ``r++;``    ``}` `    ``return` `(ans);``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 1, 2, 3, 4, 10, 11, 14, 15 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``int` `k = 4;``    ``printf``(``"%d"``, maximiseSubset(arr, n, k));``    ``return` `0;``}`

## Java

 `/* Java program to find the maximum size of subset``of points that can have consecutive values``using efficient approach */``import` `java.util.*;` `class` `GFG``{``    ``static` `int` `maximiseSubset(``int``[] arr, ``int` `n, ``int` `k)``    ``{``        ``// Since we can always enforce the``        ``// solution to contain all the K added``        ``// points``        ``int` `ans = k;` `        ``int` `l = ``0``, r = ``0``;``        ``while` `(r < n) {` `            ``// increment l until the number of points``            ``// that need to be placed between index l``            ``// and index r is not greater than k``            ``while` `((arr[r] - arr[l]) - (r - l) > k)``                ``l++;``        ` `            ``// update the solution as below``            ``ans = Math.max(ans, r - l + k + ``1``);``        ` `            ``r++;``        ``}` `        ``return` `(ans);``    ``}` `    ``// Driver code ``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int``[] arr = { ``1``, ``2``, ``3``, ``4``, ``10``, ``11``, ``14``, ``15` `};``        ``int` `n = arr.length;``        ``int` `k = ``4``;``        ``System.out.println(maximiseSubset(arr, n, k));``    ``}``}``/* This code is contributed by Mr. Somesh Awasthi */`

## Python3

 `# Python 3 program to find the maximum size``# of subset of points that can have consecutive``# values using efficient approach``def` `maximiseSubset(arr, n, k):` `    ``# Since we can always enforce the solution``    ``# to contain all the K added points``    ``ans ``=` `k;` `    ``l ``=` `0``; r ``=` `0``;``    ``while` `(r < n):` `        ``# increment l until the number of points``        ``# that need to be placed between index l``        ``# and index r is not greater than k``        ``while` `((arr[r] ``-` `arr[l]) ``-` `(r ``-` `l) > k):``            ``l ``=` `l ``+` `1``;``        ` `        ``# update the solution as below``        ``ans ``=` `max``(ans, r ``-` `l ``+` `k ``+` `1``);``        ` `        ``r ``=` `r ``+` `1``;``        ` `    ``return` `(ans);` `# Driver code``arr ``=` `[ ``1``, ``2``, ``3``, ``4``, ``10``, ``11``, ``14``, ``15` `];``n ``=` `len``(arr);``k ``=` `4``;``print``(maximiseSubset(arr, n, k));` `# This code is contributed``# by Akanksha Rai`

## C#

 `/* C# program to find the``maximum size of subset``of points that can have``consecutive values using``efficient approach */``using` `System;` `class` `GFG``{``    ``static` `int` `maximiseSubset(``int``[] arr,``                              ``int` `n, ``int` `k)``    ``{``        ``// Since we can always enforce``        ``// the solution to contain all``        ``// the K added points``        ``int` `ans = k;` `        ``int` `l = 0, r = 0;``        ``while` `(r < n)``        ``{` `            ``// increment l until the``            ``// number of points that``            ``// need to be placed``            ``// between index l and``            ``// index r is not greater``            ``// than k``            ``while` `((arr[r] - arr[l]) -``                        ``(r - l) > k)``                ``l++;``        ` `            ``// update the``            ``// solution as below``            ``ans = Math.Max(ans, r - l +``                                ``k + 1);``        ` `            ``r++;``        ``}` `        ``return` `(ans);``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int``[] arr = {1, 2, 3, 4,``                    ``10, 11, 14, 15};``        ``int` `n = arr.Length;``        ``int` `k = 4;``        ``Console.WriteLine(maximiseSubset(arr, n, k));``    ``}``}` `// This code is contributed``// by anuj_67.`

## PHP

 ` ``\$k``)``            ``\$l``++;``    ` `        ``// update the solution as below``        ``\$ans` `= max(``\$ans``, ``\$r` `- ``\$l` `+ ``\$k` `+ 1);``    ` `        ``\$r``++;``    ``}` `    ``return` `(``\$ans``);``}` `// Driver code``\$arr` `= ``array``(1, 2, 3, 4, 10, 11, 14, 15 );``\$n` `= sizeof(``\$arr``);``\$k` `= 4;``echo``(maximiseSubset(``\$arr``, ``\$n``, ``\$k``));` `// This code is contributed by Mukul Singh``?>`

## Javascript

 ``

Output:

`8`

Time Complexity: O(N)

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