Syntax error Program to check regular expression pattern is matching with string or not in Python

Program to check regular expression pattern is matching with string or not in Python

Suppose we have a string s and a regular expression pattern. We have to check whether the given pattern matches with given string or not. In the regular expression, there are few rules −

  • . (period) which matches any single character

  • * (asterisk) which matches zero or more of the preceding element.

So, if the input is like pattern = "h.l*o" s = "hello", then the output will be True, as We have ra and then a single character

To solve this, we will follow these steps −

  • n := size of s

  • m := size of p

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

  • if j is same as m, then

    • return i is same as n

  • match := true when (i < n and(s[i] is same as p[j] or p[j] is same as ".") otherwise false

  • if j + 1 & m and p[j + 1] is same as "*", then

    • return true when dp(i, j + 2) or (match and dp(i + 1, j)) otherwise false

  • return match and dp(i + 1, j + 1)

  • From the main method return dp(0, 0)

Example  

Let us see the following implementation to get better understanding −

 Live Demo

class Solution:
   def solve(self, p, s):
      n = len(s)
      m = len(p)
      def dp(i, j):
         if j == m:
            return i == n
         match = i < n and (s[i] == p[j] or p[j] == ".")
         if j + 1 < m and p[j + 1] == "*":
            return dp(i, j + 2) or (match and dp(i + 1, j))
         return match and dp(i + 1, j + 1)
      return dp(0, 0)
ob = Solution()
pattern = "h.l*o"
s = "hello"
print(ob.solve(pattern, s))

Input

"h.l*o", "hello"

Output

True
Updated on: 2020-12-22T08:41:32+05:30

573 Views

Kickstart Your Career

Get certified by completing the course

Get Started
Advertisements