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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 <iostream>
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




<?php
// PHP code for finding the
// longest length integer
 
function longestInteger($str, $l)
{
    $count = 0;
    $max = 0;
    $pos = -1;
    $pre_pos = 0;
    $pre_len = 0;
    $len = 0;
     
    // Traverse the string
    for ($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 (is_numeric($str[$i]))
            $pos = $i;
 
        // Traverse the string till
        // a character occurs.
        while (is_numeric($str[$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 = $pre_len;
        }
    }
    return (substr($str, $pos, $len));
}
 
// Driver code
$str = "geeks100for1234geeks";
$l = strlen($str);
echo longestInteger($str, $l);
 
// This code is contributed
// by ChitraNayal
?>

Javascript




<script>
// Javascript code for finding the
// longest length integer
     
    function longestInteger(str,l)
    {
        let count = 0, max = 0,
        pos = -1, pre_pos,
        pre_len, len = 0;
       
    // Traverse the string
    for (let 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 (!isNaN(String(str[i]) * 1))
            pos = i;
   
        // Traverse the string
        // till a character occurs.
        while (!isNaN(String(str[i]) * 1))
        {
            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
    let str = "geeks100for1234geeks";
    let l = str.length;
    document.write(longestInteger(str, l));
     
 
// This code is contributed by rag2127
</script>
Output: 
1234

 

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


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