Program to count number of palindromic substrings in Python

Suppose we have a string s, we have to find the number of palindromic substrings in s.

So, if the input is like s = "level", then the output will be 7, as the palindromic substrings are: ["l","e","v","e","l","eve","level"]

To solve this, we will follow these steps −

• Define a function check_palindrome(). This will take string, left, right
• ans := 0
• while left >= 0 and right < size of s, do
• if s[left] is same as s[right], then
• ans := ans + 1
• left := left - 1
• right := right + 1
• otherwise,
• return ans
• return ans
• From the main method, do the following −
• ans := 0
• for char_index in range 0 to size of s, do
• ans := ans + check_palindrome(s, char_index - 1, char_index + 1)
• ans := ans + check_palindrome(s, char_index, char_index + 1)
• return (ans) + size of s

Let us see the following implementation to get better understanding −

Example

Live Demo

class Solution:
def solve(self, s):
def check_palindrome(string, left, right):
ans = 0
while left >= 0 and right < len(s):
if s[left] == s[right]:
ans += 1
left -= 1
right += 1
else:
return ans
return ans
ans = 0
for char_index in range(len(s)):
ans += check_palindrome(s, char_index - 1, char_index + 1)
ans += check_palindrome(s, char_index, char_index + 1)
return (ans) + len(s)
ob = Solution()
print(ob.solve("level"))

Input

"level"

Output

7

Updated on: 19-Oct-2020

2K+ Views