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Python – Longest Substring Length of K

  • Last Updated : 02 Sep, 2020

Given a String and a character K, find longest substring length of K.

Input : test_str = ‘abcaaaacbbaa’, K = b
Output : 2
Explanation : b occurs twice, 2 > 1.

Input : test_str = ‘abcaacccbbaa’, K = c
Output : 3
Explanation : Maximum times c occurs is 3.

Method #1 : Using loop

This is brute way to solve this problem, in this, when K is encountered, counter is maintained till other character occurs, and count is noted, the maximum of these counts is kept and is returned as result.

Python3




# Python3 code to demonstrate working of 
# Longest Substring of K
# Using loop
  
# initializing string
test_str = 'abcaaaacbbaa'
  
# printing original String
print("The original string is : " + str(test_str))
  
# initializing K 
K = 'a'
  
cnt = 0
res = 0
for idx in range(len(test_str)):
      
    # increment counter on checking
    if test_str[idx] == K:
        cnt += 1
    else:
        cnt = 0
          
    # retaining max
    res = max(res, cnt)
  
# printing result 
print("The Longest Substring Length : " + str(res)) 
Output
The original string is : abcaaaacbbaa
The Longest Substring Length : 4

Method #2 : Using findall() + max()

In this, we get all the possible substrings of K using findall() and max() is used over it to get maximum length with len as key.

Python3




# Python3 code to demonstrate working of 
# Longest Substring of K
# Using findall() + max()
import re
  
# initializing string
test_str = 'abcaaaacbbaa'
  
# printing original String
print("The original string is : " + str(test_str))
  
# initializing K 
K = 'a'
  
# getting all substrings
res = re.findall(r'' + K + '+', test_str)
  
# getting maximum of substrings Length
res = len(max(res, key = len))
  
# printing result 
print("The Longest Substring Length : " + str(res)) 
Output
The original string is : abcaaaacbbaa
The Longest Substring Length : 4


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