# Find longest length number in a string

• Difficulty Level : Medium
• Last Updated : 12 May, 2021

Given a string of digits and characters. Write a program to find the number with the maximum number of digits in a string.
Note: The number may not be the greatest number in the string. For example, if the string is “a123bc321” then the answer can be 123 or 321 as the problem is to find the number with the longest length and not the largest value.
Examples:

```Input: geeks100for1234geeks
Output: 1234

Input: abx12321bst1234yz
Output: 12321```

Approach: The idea is to traverse the string and if a digit is encountered, store its position and from that position traverse further until a character occurs. Every time a continuous series of a digit is encountered, store its length and match it with the length previously find series of a digit to find out the maximum of all the continuous series of digits.
Below is the implementation of above approach.

## C++

 `// C++ code for finding the longest``// length integer``#include ``using` `namespace` `std;` `string longestInteger(string str, ``int` `l)``{``    ``int` `count = 0, max = 0, pos = -1, pre_pos, pre_len, len = 0;``    ``// Traverse the string``    ``for` `(``int` `i = 0; i < l; i++) {``        ``// Store the previous position and previous length``        ``// of the digits encountered.``        ``pre_pos = pos;``        ``pre_len = len;``        ``count = 0;``        ``len = 0;` `        ``// If first digit occurs, store its position in pos``        ``if` `(``isdigit``(str[i]))``            ``pos = i;` `        ``// Traverse the string till a character occurs.``        ``while` `(``isdigit``(str[i])) {``            ``count++;``            ``i++;``            ``len++;``        ``}` `        ``// Check if the length of the string is``        ``// greater than the previous ones or not.``        ``if` `(count > max) {``            ``max = count;``        ``}``        ``else` `{``            ``pos = pre_pos;``            ``len = pre_len;``        ``}``    ``}``    ``return` `(str.substr(pos, len));``}` `// Driver code``int` `main()``{``    ``string str = ``"geeks100for1234geeks"``;``    ``int` `l = str.length();``    ``cout << longestInteger(str, l);``    ``return` `0;``}`

## Java

 `// Java code for finding the``// longest length integer``import` `java.io.*;``import` `java.util.*;``import` `java.lang.*;` `class` `GFG``{``static` `String longestInteger(String str, ``int` `l)``{``    ``int` `count = ``0``, max = ``0``,``        ``pos = -``1``, pre_pos,``        ``pre_len, len = ``0``;``    ` `    ``// Traverse the string``    ``for` `(``int` `i = ``0``; i < l; i++)``    ``{``        ``// Store the previous position``        ``// and previous length of the``        ``// digits encountered.``        ``pre_pos = pos;``        ``pre_len = len;``        ``count = ``0``;``        ``len = ``0``;` `        ``// If first digit occurs,``        ``// store its position in pos``        ``if` `(Character.isDigit(str.charAt(i)))``            ``pos = i;` `        ``// Traverse the string``        ``// till a character occurs.``        ``while` `(Character.isDigit(str.charAt(i)))``        ``{``            ``count++;``            ``i++;``            ``len++;``        ``}` `        ``// Check if the length of``        ``// the string is greater``        ``// than the previous ones``        ``// or not.``        ``if` `(count > max)``        ``{``            ``max = count;``        ``}``        ``else``        ``{``            ``pos = pre_pos;``            ``len = pre_len;``        ``}``    ``}``    ``return` `(str.substring(pos, pos + len));``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``String str = ``"geeks100for1234geeks"``;``    ``int` `l = str.length();``    ``System.out.print(longestInteger(str, l));``}``}`

## C#

 `// C# code for finding the``// longest length integer``using` `System;` `class` `GFG``{``static` `string` `longestInteger(``string` `str,``                             ``int` `l)``{``    ``int` `count = 0, max = 0,``        ``pos = -1, pre_pos,``        ``pre_len, len = 0;``    ` `    ``// Traverse the string``    ``for` `(``int` `i = 0; i < l; i++)``    ``{``        ``// Store the previous position``        ``// and previous length of the``        ``// digits encountered.``        ``pre_pos = pos;``        ``pre_len = len;``        ``count = 0;``        ``len = 0;` `        ``// If first digit occurs,``        ``// store its position in pos``        ``if` `(Char.IsDigit(str[i]))``            ``pos = i;` `        ``// Traverse the string``        ``// till a character occurs.``        ``while` `(Char.IsDigit(str[i]))``        ``{``            ``count++;``            ``i++;``            ``len++;``        ``}` `        ``// Check if the length of``        ``// the string is greater``        ``// than the previous ones``        ``// or not.``        ``if` `(count > max)``        ``{``            ``max = count;``        ``}``        ``else``        ``{``            ``pos = pre_pos;``            ``len = pre_len;``        ``}``    ``}``    ``return` `(str.Substring(pos, len));``}` `// Driver code``public` `static` `void` `Main()``{``    ``string` `str = ``"geeks100for1234geeks"``;``    ``int` `l = str.Length;``    ``Console.Write(longestInteger(str, l));``}``}` `// This code is contributed``// by ChitraNayal`

## Python 3

 `# Python 3 code for finding the``# longest length integer` `def` `longestInteger(s, length):``    ``count ``=` `0``    ``maximum ``=` `0``    ``pos ``=` `-``1``    ``l ``=` `0``    ` `    ``# Traverse the string``    ``for` `i ``in` `range``(length):``        ` `        ``# Store the previous position``        ``# and previous length of``        ``# the digits encountered.``        ``pre_pos ``=` `pos``        ``pre_len ``=` `l``        ``count ``=` `0``        ``l ``=` `0` `        ``# If first digit occurs,``        ``# store its position in pos``        ``if` `(s[i].isdecimal()):``            ``pos ``=` `i` `        ``# Traverse the string``        ``# till a character occurs.``        ``while` `(s[i].isdecimal()):``            ``count ``+``=` `1``            ``i ``+``=` `1``            ``l ``+``=` `1` `        ``# Check if the length of``        ``# the string is greater``        ``# than the previous ones``        ``# or not.``        ``if` `(count > maximum):``            ``maximum ``=` `count``        ` `        ``else``:``            ``pos ``=` `pre_pos``            ``l ``=` `pre_len` `    ``return` `(s[pos: pos ``+` `l])` `# Driver code``s ``=` `"geeks100for1234geeks"``length ``=` `len``(s)``print``(longestInteger(s, length))` `# This code is contributed``# by ChitraNayal`

## PHP

 ` ``\$max``)``        ``{``            ``\$max` `= ``\$count``;``        ``}``        ``else``        ``{``            ``\$pos` `= ``\$pre_pos``;``            ``\$len` `= ``\$pre_len``;``        ``}``    ``}``    ``return` `(``substr``(``\$str``, ``\$pos``, ``\$len``));``}` `// Driver code``\$str` `= ``"geeks100for1234geeks"``;``\$l` `= ``strlen``(``\$str``);``echo` `longestInteger(``\$str``, ``\$l``);` `// This code is contributed``// by ChitraNayal``?>`

## Javascript

 ``
Output:
`1234`

Time Complexity: O(n)
Auxiliary Space Complexity: O(1)

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