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Longest substring such that no three consecutive characters are same
  • Difficulty Level : Medium
  • Last Updated : 23 Sep, 2019

Given string str, the task is to find the length of the longest substring of str such that no three consecutive characters in the substring are same.

Examples:

Input: str = “baaabbabbb”
Output: 7
“aabbabb” is the required substring.

Input: str = “babba”
Output: 5
Given string itself is the longest substring.

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



  • If the length of the given string is less than 3 then the length of the string will be the answer.
  • Initialize temp and ans as 2 initially, since this is the minimum length of the longest substring when the length of the given string is greater than 2.
  • Iterate in the string from 2 to N – 1 and increment temp by 1 if str[i] != str[i – 1] or str[i] != str[i – 2].
  • Else re-initialize temp = 2 and ans = max(ans, temp).

Below is the implementation of the above approach:

C++

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// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to return the length of the
// longest substring such that no three
// consecutive characters are same
int maxLenSubStr(string& s)
{
    // If the length of the given string
    // is less than 3
    if (s.length() < 3)
        return s.length();
  
    // Initialize temporary and final ans
    // to 2 as this is the minimum length
    // of substring when length of the given
    // string is greater than 2
    int temp = 2;
    int ans = 2;
  
    // Traverse the string from the
    // third character to the last
    for (int i = 2; i < s.length(); i++) {
  
        // If no three consecutive characters
        // are same then increment temporary count
        if (s[i] != s[i - 1] || s[i] != s[i - 2])
            temp++;
  
        // Else update the final ans and
        // reset the temporary count
        else {
            ans = max(temp, ans);
            temp = 2;
        }
    }
  
    ans = max(temp, ans);
  
    return ans;
}
  
// Driver code
int main()
{
    string s = "baaabbabbb";
  
    cout << maxLenSubStr(s);
  
    return 0;
}

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Java

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// Java implementation of the approach
import java.util.*;
  
class GFG 
{
  
// Function to return the length of the
// longest substring such that no three
// consecutive characters are same
static int maxLenSubStr(String s)
{
    // If the length of the given string
    // is less than 3
    if (s.length() < 3)
        return s.length();
  
    // Initialize temporary and final ans
    // to 2 as this is the minimum length
    // of substring when length of the given
    // string is greater than 2
    int temp = 2;
    int ans = 2;
  
    // Traverse the string from the
    // third character to the last
    for (int i = 2; i < s.length(); i++) 
    {
  
        // If no three consecutive characters
        // are same then increment temporary count
        if (s.charAt(i) != s.charAt(i - 1) ||
            s.charAt(i) != s.charAt(i - 2))
            temp++;
  
        // Else update the final ans and
        // reset the temporary count
        else
        {
            ans = Math.max(temp, ans);
            temp = 2;
        }
    }
    ans = Math.max(temp, ans);
  
    return ans;
}
  
// Driver code
public static void main(String[] args)
{
    String s = "baaabbabbb";
  
    System.out.println(maxLenSubStr(s));
}
  
// This code is contributed by PrinciRaj1992

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Python3

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# Python3 implementation of the approach
  
# Function to return the length of the
# longest substring such that no three
# consecutive characters are same
def maxLenSubStr(s):
      
    # If the length of the given string
    # is less than 3
    if (len(s) < 3):
        return len(s)
  
    # Initialize temporary and final ans
    # to 2 as this is the minimum length
    # of substring when length of the given
    # string is greater than 2
    temp = 2
    ans = 2
  
    # Traverse the string from the
    # third character to the last
    for i in range(2, len(s)):
  
        # If no three consecutive characters
        # are same then increment temporary count
        if (s[i] != s[i - 1] or s[i] != s[i - 2]):
            temp += 1
  
        # Else update the final ans and
        # reset the temporary count
        else:
            ans = max(temp, ans)
            temp = 2
    ans = max(temp, ans)
  
    return ans
  
# Driver code
s = "baaabbabbb"
  
print(maxLenSubStr(s))
  
# This code is contributed by Mohit Kumar

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C#

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// C# implementation of the approach
using System;
  
class GFG
{
      
// Function to return the length of the
// longest substring such that no three
// consecutive characters are same
static int maxLenSubStr(String s)
{
    // If the length of the given string
    // is less than 3
    if (s.Length < 3)
        return s.Length;
  
    // Initialize temporary and final ans
    // to 2 as this is the minimum length
    // of substring when length of the given
    // string is greater than 2
    int temp = 2;
    int ans = 2;
  
    // Traverse the string from the
    // third character to the last
    for (int i = 2; i < s.Length; i++) 
    {
  
        // If no three consecutive characters
        // are same then increment temporary count
        if (s[i] != s[i - 1] ||
            s[i] != s[i - 2])
            temp++;
  
        // Else update the final ans and
        // reset the temporary count
        else
        {
            ans = Math.Max(temp, ans);
            temp = 2;
        }
    }
    ans = Math.Max(temp, ans);
  
    return ans;
}
  
// Driver code
static public void Main ()
{
    String s = "baaabbabbb"
    Console.Write(maxLenSubStr(s));
}
  
// This code is contributed by ajit.

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Output:

7

Time Complexity: O(N) where N is the length of the string.
Space Complexity: O(1)

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