# Program to find length of longest substring with character count of at least k in Python

PythonServer Side ProgrammingProgramming

Suppose we have a string s where each characters are sorted and we also have a number k, we have to find the length of the longest substring such that every character occurs at least k times.

So, if the input is like s = "aabccddeeffghij" k = 2, then the output will be 8, as the longest substring here is "ccddeeff" here every character occurs at least 2 times.

To solve this, we will follow these steps −

• Define a function rc() . This will take lst
• c := a map with all characters and their occurrences
• acc := a new list
• ans := 0
• valid := True
• for each x in lst, do
• if c[x] < k, then
• valid := False
• ans := maximum of ans and rc(acc)
• acc := a new list
• otherwise,
• insert x at the end of acc
• if valid true, then
• return size of acc
• otherwise,
• ans := maximum of ans and rc(acc)
• return ans
• From the main method, do the following −
• return rc(a new list by converting each character of s)

Let us see the following implementation to get better understanding −

## Example

Live Demo

from collections import Counter
class Solution:
def solve(self, s, k):
def rc(lst):
c = Counter(lst)
acc = []
ans = 0
valid = True
for x in lst:
if c[x] < k:
valid = False
ans = max(ans, rc(acc))
acc = []
else:
acc.append(x)
if valid:
return len(acc)
else:
ans = max(ans, rc(acc))
return ans
return rc(list(s))
ob = Solution()
s = "aabccddeeffghij"
k = 2
print(ob.solve(s, k))

## Input

"aabccddeeffghij", 2

## Output

8