Suppose we have a number k and another string s, we have to find the size of the longest substring that contains at most k distinct characters.
So, if the input is like k = 3 s = "kolkata", then the output will be 4, as there are two longest substrings with 3 distinct characters these are "kolk" and "kata", which have length 4.
To solve this, we will follow these steps −
ans := 0, left := 0
table := a new map
for right is in range 0 to size of s − 1, do
table[s[right]] := 1 + (s[right] if exists otherwise 0)
if size of table <= k, then
ans := maximum of ans and (right − left + 1)
otherwise,
while size of table > k, do
left_char := s[left]
if table[left_char] is same as 1, then
delete left_char−th element from table
otherwise,
table[left_char] := table[left_char] − 1
left := left + 1
return ans
Let us see the following implementation to get better understanding −
Example
class Solution: def solve(self, k, s): ans = 0 left = 0 table = {} for right in range(0, len(s)): table[s[right]] = table.get(s[right], 0) + 1 if len(table) <= k: ans = max(ans, right − left + 1) else: while len(table) > k: left_char = s[left] if table[left_char] == 1: table.pop(left_char) else: table[left_char] −= 1 left += 1 return ans ob = Solution() k = 3 s = "kolkata" print(ob.solve(k, s))
Input
"anewcoffeepot"
Output
4