Length of the longest substring with no consecutive same letters

Given a string str, the task is to find the length of the longest sub-string which does not have any pair of consecutive same characters.

Examples:

Input: str = “abcdde”
Output: 4
“abcd” is the longest

Input: str = “ccccdeededff”
Output: 5
“ededf” is the longest

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

Approach: The following steps can be followed to solve the above problem:

Initialize cnt and maxi as 1 initially, since this is the minimum answer of the length of the longest answer.
Iterate in the string from 1 to n – 1 and increment cnt by 1 if str[i] != str[i – 1].
If str[i] == str[i – 1], then re-initialize cnt as 1 and maxi to max(maxi, cnt).

Below is the implementation of the above approach:

C++

// C++ implementation of the approach 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to return the length 
// of the required sub-string 
int longestSubstring(string s) 
{ 
    int cnt = 1; 
    int maxi = 1; 
  
    // Get the length of the string 
    int n = s.length(); 
  
    // Iterate in the string 
    for (int i = 1; i < n; i++) { 
  
        // Check for not consecutive 
        if (s[i] != s[i - 1]) 
            cnt++; 
        else { 
  
            // If cnt greater than maxi 
            maxi = max(cnt, maxi); 
  
            // Re-initialize 
            cnt = 1; 
        } 
    } 
  
    // Check after iteration 
    // is complete 
    maxi = max(cnt, maxi); 
  
    return maxi; 
} 
  
// Driver code 
int main() 
{ 
    string s = "ccccdeededff"; 
    cout << longestSubstring(s); 
  
    return 0; 
} 

Java

// Java implementation of the approach  
import java.lang.Math; 
  
class GfG 
{ 
  
    // Function to return the length  
    // of the required sub-string  
    static int longestSubstring(String s)  
    {  
        int cnt = 1, maxi = 1;  
      
        // Get the length of the string  
        int n = s.length();  
      
        // Iterate in the string  
        for (int i = 1; i < n; i++)  
        {  
      
            // Check for not consecutive  
            if (s.charAt(i) != s.charAt(i-1))  
                cnt++;  
            else 
            {  
      
                // If cnt greater than maxi  
                maxi = Math.max(cnt, maxi);  
      
                // Re-initialize  
                cnt = 1;  
            }  
        }  
      
        // Check after iteration is complete  
        maxi = Math.max(cnt, maxi);  
      
        return maxi;  
    }  
  
    // Driver code 
    public static void main(String []args) 
    { 
          
        String s = "ccccdeededff"; 
        System.out.println(longestSubstring(s)); 
    } 
} 
  
// This code is contributed by Rituraj Jain 

C#

// C# implementation of the approach  
using System; 
  
class GfG  
{  
  
    // Function to return the length  
    // of the required sub-string  
    static int longestSubstring(string s)  
    {  
        int cnt = 1, maxi = 1;  
      
        // Get the length of the string  
        int n = s.Length;  
      
        // Iterate in the string  
        for (int i = 1; i < n; i++)  
        {  
      
            // Check for not consecutive  
            if (s[i] != s[i - 1])  
                cnt++;  
            else
            {  
      
                // If cnt greater than maxi  
                maxi = Math.Max(cnt, maxi);  
      
                // Re-initialize  
                cnt = 1;  
            }  
        }  
      
        // Check after iteration is complete  
        maxi = Math.Max(cnt, maxi);  
      
        return maxi;  
    }  
  
    // Driver code  
    static void Main()  
    {  
          
        string s = "ccccdeededff";  
        Console.WriteLine(longestSubstring(s));  
    }  
}  
  
// This code is contributed by mits 

Python3

# Python3 implementation of the approach  
  
# Function to return the length  
# of the required sub-string  
def longestSubstring(s) : 
  
    cnt = 1;  
    maxi = 1;  
  
    # Get the length of the string  
    n = len(s);  
  
    # Iterate in the string  
    for i in range(1, n) :  
  
        # Check for not consecutive  
        if (s[i] != s[i - 1]) : 
            cnt += 1;  
              
        else : 
              
            # If cnt greater than maxi  
            maxi = max(cnt, maxi);  
  
            # Re-initialize  
            cnt = 1;  
  
    # Check after iteration  
    # is complete  
    maxi = max(cnt, maxi);  
  
    return maxi;  
  
# Driver code  
if __name__ == "__main__" : 
      
    s = "ccccdeededff"; 
    print(longestSubstring(s));  
      
# This code is contirbuted by Ryuga 

PHP

<?php 
// PHP implementation of the approach 
  
// Function to return the length 
// of the required sub-string 
function longestSubstring($s) 
{ 
    $cnt = 1; 
    $maxi = 1; 
  
    // Get the length of the string 
    $n = strlen($s); 
  
    // Iterate in the string 
    for ($i = 1; $i < $n; $i++) 
    { 
  
        // Check for not consecutive 
        if ($s[$i] != $s[$i - 1]) 
            $cnt++; 
        else
        { 
  
            // If cnt greater than maxi 
            $maxi = max($cnt, $maxi); 
  
            // Re-initialize 
            $cnt = 1; 
        } 
    } 
  
    // Check after iteration 
    // is complete 
    $maxi = max($cnt, $maxi); 
  
    return $maxi; 
} 
  
// Driver code 
$s = "ccccdeededff"; 
echo longestSubstring($s); 
  
// This code is contributed by Akanksha Rai 
?> 

Output:

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My Personal Notes

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

C++

Java

C#

Python3

PHP

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