Related Articles

# Maximum consecutive numbers present in an array

• Difficulty Level : Easy
• Last Updated : 29 Aug, 2021

Find the length of maximum number of consecutive numbers jumbled up in an array.
Examples:

```Input : arr[] = {1, 94, 93, 1000, 5, 92, 78};
Output : 3
The largest set of consecutive elements is
92, 93, 94

Input  : arr[] = {1, 5, 92, 4, 78, 6, 7};
Output : 4
The largest set of consecutive elements is
4, 5, 6, 7```

The idea is to use hashing. We traverse through the array and for every element, we check if it is the starting element of its sequence. If yes then by incrementing its value we search the set and increment the length. By repeating this for all elements, we can find the lengths of all consecutive sets in array. Finally we return length of the largest set.

## C++

 `// CPP program to find largest consecutive numbers``// present in arr[].``#include ``using` `namespace` `std;` `int` `findLongestConseqSubseq(``int` `arr[], ``int` `n)``{``    ``/* We insert all the array elements into``       ``unordered set. */``    ``unordered_set<``int``> S;``    ``for` `(``int` `i = 0; i < n; i++)``        ``S.insert(arr[i]);` `    ``// check each possible sequence from the start``    ``// then update optimal length``    ``int` `ans = 0;``    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// if current element is the starting``        ``// element of a sequence``        ``if` `(S.find(arr[i] - 1) == S.end()) {` `            ``// Then check for next elements in the``            ``// sequence``            ``int` `j = arr[i];` `            ``// increment the value of array element``            ``// and repeat search in the set``            ``while` `(S.find(j) != S.end())``                ``j++;` `            ``// Update  optimal length if this length``            ``// is more. To get the length as it is``            ``// incremented one by one``            ``ans = max(ans, j - arr[i]);``        ``}``    ``}``    ``return` `ans;``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 1, 94, 93, 1000, 5, 92, 78 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(``int``);``    ``cout << findLongestConseqSubseq(arr, n) << endl;``    ``return` `0;``}`

## Java

 `// Java program to find largest consecutive``// numbers present in arr[].``import` `java.util.*;` `class` `GFG``{``    ` `static` `int` `findLongestConseqSubseq(``int` `arr[], ``int` `n)``{``    ``/* We insert all the array elements into``    ``unordered set. */``    ``HashSet S = ``new` `HashSet();``    ``for` `(``int` `i = ``0``; i < n; i++)``        ``S.add(arr[i]);` `    ``// check each possible sequence from the start``    ``// then update optimal length``    ``int` `ans = ``0``;``    ``for` `(``int` `i = ``0``; i < n; i++)``    ``{` `        ``// if current element is the starting``        ``// element of a sequence``        ``if``(S.contains(arr[i]))``        ``{` `            ``// Then check for next elements in the``            ``// sequence``            ``int` `j = arr[i];` `            ``// increment the value of array element``            ``// and repeat search in the set``            ``while` `(S.contains(j))``                ``j++;` `            ``// Update optimal length if this length``            ``// is more. To get the length as it is``            ``// incremented one by one``            ``ans = Math.max(ans, j - arr[i]);``        ``}``    ``}``    ``return` `ans;``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = {``1``, ``94``, ``93``, ``1000``, ``5``, ``92``, ``78``};``    ``int` `n = arr.length;``        ``System.out.println(findLongestConseqSubseq(arr, n));``}``}` `// This code contributed by Rajput-Ji`

## Python3

 `# Python3 program to find largest consecutive``# numbers present in arr.` `def` `findLongestConseqSubseq(arr, n):``    ``'''We insert all the array elements into unordered set.'''` `    ``S ``=` `set``();``    ``for` `i ``in` `range``(n):``        ``S.add(arr[i]);` `    ``# check each possible sequence from the start``    ``# then update optimal length``    ``ans ``=` `0``;``    ``for` `i ``in` `range``(n):``        ` `        ``# if current element is the starting``        ``# element of a sequence``        ``if` `S.__contains__(arr[i]):``            ` `            ``# Then check for next elements in the``            ``# sequence``            ``j ``=` `arr[i];``            ` `            ``# increment the value of array element``            ``# and repeat search in the set``            ``while``(S.__contains__(j)):``                ``j ``+``=` `1``;` `            ``# Update optimal length if this length``            ``# is more. To get the length as it is``            ``# incremented one by one``            ``ans ``=` `max``(ans, j ``-` `arr[i]);``    ``return` `ans;` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[ ``1``, ``94``, ``93``, ``1000``, ``5``, ``92``, ``78` `];``    ``n ``=` `len``(arr);``    ``print``(findLongestConseqSubseq(arr, n));` `# This code is contributed by 29AjayKumar`

## C#

 `// C# program to find largest consecutive``// numbers present in arr[].``using` `System;``using` `System.Collections.Generic; ``public` `class` `GFG``{``    ` `static` `int` `findLongestConseqSubseq(``int` `[]arr, ``int` `n)``{``    ``/* We insert all the array elements into``    ``unordered set. */``    ``HashSet<``int``> S = ``new` `HashSet<``int``>();``    ``for` `(``int` `i = 0; i < n; i++)``        ``S.Add(arr[i]);` `    ``// check each possible sequence from the start``    ``// then update optimal length``    ``int` `ans = 0;``    ``for` `(``int` `i = 0; i < n; i++)``    ``{` `        ``// if current element is the starting``        ``// element of a sequence``        ``if``(S.Contains(arr[i]))``        ``{` `            ``// Then check for next elements in the``            ``// sequence``            ``int` `j = arr[i];` `            ``// increment the value of array element``            ``// and repeat search in the set``            ``while` `(S.Contains(j))``                ``j++;` `            ``// Update optimal length if this length``            ``// is more. To get the length as it is``            ``// incremented one by one``            ``ans = Math.Max(ans, j - arr[i]);``        ``}``    ``}``    ``return` `ans;``}` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``int` `[]arr = {1, 94, 93, 1000, 5, 92, 78};``    ``int` `n = arr.Length;``    ``Console.WriteLine(findLongestConseqSubseq(arr, n));``}``}` `// This code has been contributed by 29AjayKumar`

## Javascript

 ``

Output:

`3`

Time complexity : O(n2)

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

My Personal Notes arrow_drop_up