# Maximum length of the sub-array whose first and last elements are same

Given a character array arr[] containing only lowercase English alphabets, the task is to print the maximum length of the subarray such that the first and the last element of the sub-array are same.

Examples:

Input: arr[] = {‘g’, ‘e’, ‘e’, ‘k’, ‘s’}
Output: 2
{‘e’, ‘e’} is the maximum length sub-array satisfying the given condition.

Input: arr[] = {‘a’, ‘b’, ‘c’, ‘d’, ‘a’}
Output: 5
{‘a’, ‘b’, ‘c’, ‘d’, ‘a’} is the required sub-array

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: For every element of the array ch, store it’s first and last occurrence. Then the maximum length of the sub-array that starts and ends with the same element ch will be lastOccurrence(ch) – firstOccurrence(ch) + 1. The maximum of this value among all the elements is the required answer.

Below is the implementation of the above approach:

## Java

 `// Java implementation of the approach ` ` `  `// Class that represents a single element ` `// of the given array and stores it's first ` `// and the last occurrence in the array ` `class` `Element { ` `    ``int` `firstOcc, lastOcc; ` ` `  `    ``public` `Element() ` `    ``{ ` `        ``firstOcc = lastOcc = -``1``; ` `    ``} ` ` `  `    ``// Function to update the occurrence ` `    ``// of a particular character in the array ` `    ``public` `void` `updateOccurrence(``int` `index) ` `    ``{ ` ` `  `        ``// If first occurrence is set to something ` `        ``// other than -1 then it doesn't need updating ` `        ``if` `(firstOcc == -``1``) ` `            ``firstOcc = index; ` ` `  `        ``// Last occurrence will be updated everytime ` `        ``// the character appears in the array ` `        ``lastOcc = index; ` `    ``} ` `} ` ` `  `class` `GFG { ` ` `  `    ``// Function to return the maximum length of the ` `    ``// sub-array that starts and ends with the same element ` `    ``public` `static` `int` `maxLenSubArr(``char` `arr[], ``int` `n) ` `    ``{ ` ` `  `        ``Element elements[] = ``new` `Element[``26``]; ` `        ``for` `(``int` `i = ``0``; i < n; i++) { ` `            ``int` `ch = arr[i] - ``'a'``; ` ` `  `            ``// Initialize the current character ` `            ``// if haven't already ` `            ``if` `(elements[ch] == ``null``) ` `                ``elements[ch] = ``new` `Element(); ` ` `  `            ``// Update current character's occurrence ` `            ``elements[ch].updateOccurrence(i); ` `        ``} ` ` `  `        ``int` `maxLen = ``0``; ` `        ``for` `(``int` `i = ``0``; i < ``26``; i++) { ` ` `  `            ``// If current character appears in the given array ` `            ``if` `(elements[i] != ``null``) { ` ` `  `                ``// Length of the longest sub-array that starts ` `                ``// and ends with the same element ` `                ``int` `len = elements[i].lastOcc - elements[i].firstOcc + ``1``; ` `                ``maxLen = Math.max(maxLen, len); ` `            ``} ` `        ``} ` ` `  `        ``// Return the maximum length of ` `        ``// the required sub-array ` `        ``return` `maxLen; ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``char` `arr[] = { ``'g'``, ``'e'``, ``'e'``, ``'k'``, ``'s'` `}; ` `        ``int` `n = arr.length; ` ` `  `        ``System.out.print(maxLenSubArr(arr, n)); ` `    ``} ` `} `

## Python3

 `# Python3 implementation of the approach  ` ` `  `# Class that represents a single element  ` `# of the given array and stores it's first  ` `# and the last occurrence in the array  ` `class` `Element:  ` `     `  `    ``def` `__init__(``self``): ` `        ``self``.firstOcc ``=` `-``1` `        ``self``.lastOcc ``=` `-``1` ` `  `    ``# Function to update the occurrence  ` `    ``# of a particular character in the array  ` `    ``def` `updateOccurrence(``self``, index):  ` ` `  `        ``# If first occurrence is set to  ` `        ``# something other than -1 then it ` `        ``# doesn't need updating  ` `        ``if` `self``.firstOcc ``=``=` `-``1``:  ` `            ``self``.firstOcc ``=` `index  ` ` `  `        ``# Last occurrence will be updated  ` `        ``# everytime the character appears ` `        ``# in the array  ` `        ``self``.lastOcc ``=` `index  ` ` `  `# Function to return the maximum length  ` `# of the sub-array that starts and ends ` `# with the same element  ` `def` `maxLenSubArr(arr, n):  ` ` `  `    ``elements ``=` `[``None``] ``*` `26` `    ``for` `i ``in` `range``(``0``, n):  ` `        ``ch ``=` `ord``(arr[i]) ``-` `ord``(``'a'``)  ` ` `  `        ``# Initialize the current character  ` `        ``# if haven't already  ` `        ``if` `elements[ch] ``=``=` `None``:  ` `            ``elements[ch] ``=` `Element()  ` ` `  `        ``# Update current character's occurrence  ` `        ``elements[ch].updateOccurrence(i)  ` `         `  `    ``maxLen ``=` `0` `    ``for` `i ``in` `range``(``0``, ``26``):  ` ` `  `        ``# If current character appears in ` `        ``# the given array  ` `        ``if` `elements[i] !``=` `None``:  ` ` `  `            ``# Length of the longest sub-array that  ` `            ``# starts and ends with the same element  ` `            ``length ``=` `(elements[i].lastOcc ``-`  `                      ``elements[i].firstOcc ``+` `1``) ` `            ``maxLen ``=` `max``(maxLen, length)  ` `             `  `    ``# Return the maximum length of  ` `    ``# the required sub-array  ` `    ``return` `maxLen  ` `     `  `# Driver code  ` `if` `__name__ ``=``=` `"__main__"``: ` `     `  `    ``arr ``=` `[``'g'``, ``'e'``, ``'e'``, ``'k'``, ``'s'``]  ` `    ``n ``=` `len``(arr)  ` ` `  `    ``print``(maxLenSubArr(arr, n))  ` `     `  `# This code is contributed by Rituraj Jain `

## C#

 `// C# implementation of the above approach  ` `using` `System; ` ` `  `// Class that represents a single element  ` `// of the given array and stores it's first  ` `// and the last occurrence in the array  ` `public` `class` `Element  ` `{  ` `     `  `    ``public` `int` `firstOcc, lastOcc;  ` ` `  `    ``public` `Element()  ` `    ``{  ` `        ``firstOcc = lastOcc = -1;  ` `    ``}  ` ` `  `    ``// Function to update the occurrence  ` `    ``// of a particular character in the array  ` `    ``public` `void` `updateOccurrence(``int` `index)  ` `    ``{  ` ` `  `        ``// If first occurrence is set to something  ` `        ``// other than -1 then it doesn't need updating  ` `        ``if` `(firstOcc == -1)  ` `            ``firstOcc = index;  ` ` `  `        ``// Last occurrence will be updated everytime  ` `        ``// the character appears in the array  ` `        ``lastOcc = index;  ` `    ``}  ` `}  ` ` `  `class` `GFG  ` `{  ` ` `  `    ``// Function to return the maximum  ` `    ``// length of the sub-array that ` `    ``//  starts and ends with the same element  ` `    ``public` `static` `int` `maxLenSubArr(``char` `[]arr, ``int` `n)  ` `    ``{  ` ` `  `        ``Element []elements = ``new` `Element;  ` `        ``for` `(``int` `i = 0; i < n; i++)  ` `        ``{  ` `            ``int` `ch = arr[i] - ``'a'``;  ` ` `  `            ``// Initialize the current character  ` `            ``// if haven't already  ` `            ``if` `(elements[ch] == ``null``)  ` `                ``elements[ch] = ``new` `Element();  ` ` `  `            ``// Update current character's occurrence  ` `            ``elements[ch].updateOccurrence(i);  ` `        ``}  ` ` `  `        ``int` `maxLen = 0;  ` `        ``for` `(``int` `i = 0; i < 26; i++)  ` `        ``{  ` ` `  `            ``// If current character appears  ` `            ``// in the given array  ` `            ``if` `(elements[i] != ``null``) ` `            ``{  ` ` `  `                ``// Length of the longest sub-array that starts  ` `                ``// and ends with the same element  ` `                ``int` `len = elements[i].lastOcc - elements[i].firstOcc + 1;  ` `                ``maxLen = Math.Max(maxLen, len);  ` `            ``}  ` `        ``}  ` ` `  `        ``// Return the maximum length of  ` `        ``// the required sub-array  ` `        ``return` `maxLen;  ` `    ``}  ` ` `  `    ``// Driver code  ` `    ``public` `static` `void` `Main()  ` `    ``{  ` `        ``char` `[]arr = { ``'g'``, ``'e'``, ``'e'``, ``'k'``, ``'s'` `};  ` `        ``int` `n = arr.Length;  ` ` `  `        ``Console.WriteLine(maxLenSubArr(arr, n));  ` `    ``}  ` `}  ` ` `  `// This code is contributed by Ryuga `

Output:

```2
```

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Improved By : rituraj_jain, AnkitRai01