Syntax error Program to find length of longest substring with even vowel counts in Python

Program to find length of longest substring with even vowel counts in Python

Suppose we have a string s (lowercase), we have to find the length of the longest substring where each vowel occurs even number of times.

So, if the input is like s = "anewcoffeepot", then the output will be 10, as the substring "wcoffeepot" has two vowels "o" and "e", both of which occurs two times.

To solve this, we will follow these steps −

  • vowels := a map assigning vowels and numeric values as {a:0, e:1, i:2, o:3, u:4}

  • prefix := an empty map and insert a key-value pair (0, −1) into it

  • mask := 0, n := size of s, res := 0

  • for i in range 0 to n, do

    • if s[i] is a vowels, then

      • mask := mask XOR (2^vowels[s[i]])

    • if mask is not in prefix, then

      • prefix[mask] := i

    • otherwise,

      • res := maximum of res and (i − prefix[mask])

  • return res

Let us see the following implementation to get better understanding −

Example

 Live Demo

class Solution:
   def solve(self, s):
      vowels = {"a": 0, "e": 1, "i": 2, "o": 3, "u": 4}
      prefix = {0: −1}
      mask = 0
      n = len(s)
      res = 0
      for i in range(n):
         if s[i] in vowels:
            mask ^= 1 << vowels[s[i]]
         if mask not in prefix:
            prefix[mask] = i
         else:
            res = max(res, i − prefix[mask])
      return res
ob = Solution()
s = "anewcoffeepot"
print(ob.solve(s))

Input

"anewcoffeepot"

Output

10
Updated on: 2020-12-15T12:36:37+05:30

419 Views

Kickstart Your Career

Get certified by completing the course

Get Started
Advertisements