Find Possible Number of Palindromes by Trimming String in Python

Suppose we have a string s, we have to find the number of ways we can obtain a palindrome by trimming the left and right sides of s.

So, if the input is like s = "momo", then the output will be 6, as You can get ["mom", "omo", "o", "o", "m", "m", "o")

To solve this, we will follow these steps −

• Define a function expand() . This will take i, j, s

• c := 0

• while i >= 0 and j < size of s and s[i] is same as s[j], do

  • i := i − 1, j := j + 1

  • c := c + 1

• return c

• From the main method, do the following

• c := 0

• for i in range 0 to size of s, do

  • c := c + expand(i, i, s)

  • c := c + expand(i, i + 1, s)

• return c

Let us see the following implementation to get better understanding −

Example

 Live Demo

def expand(i, j, s):
   c = 0
   while i >= 0 and j < len(s) and s[i] == s[j]:
      i −= 1
      j += 1
      c += 1
   return c
class Solution:
   def solve(self, s):
      c = 0
      for i in range(len(s)):
         c += expand(i, i, s)
         c += expand(i, i + 1, s)
      return c
ob = Solution()
s = "momo"
print(ob.solve(s))

Input

"momo"

Output

6