Wildcard Pattern Matching

For this problem, one main string and another wildcard patterns are given. In this algorithm, it will check whether the wildcard pattern is matching with the main text or not.

The wildcard pattern may contain letters or ‘*’ or ‘?’ Symbols. The ‘?’ Is used to match a single character and ‘*’ is used to match the sequence of characters including empty space.

When the character is ‘*’: We can ignore the star character and move to check next characters in the pattern.

When the next character is ‘?’, then we can ignore only the current character in the text, and check for the next character in pattern and text.

When the pattern character is other than ‘*’ and ‘?’, then if the current character of pattern and text is matching, then only move further.

Input and Output

Input:
The main string and the wildcard pattern.
Main String “Algorithm”
Pattern “A*it?m”
Output:
The pattern matched.

Algorithm

wildcardMatch(text, pattern)

Input: The main text and the pattern.

Output: True when wildcard patterns matched for the main text.

Begin
   n := length of the text
   m := length of pattern

   if m = 0, then
      return 0 if n = 0, otherwise return 1
   i := 0, j := 0

   while i < n, do
      if text[i] == pattern[i], then
         increase i by 1
         increase j by 1
      else if j < m and pattern[j] is ? mark, then
         increase i by 1
         increase j by 1
      else if j < m and pattern[j] is * symbol, then
         textPointer := i
         patPointer := j
         increase j by 1
      else if patPointer is already updated, then
         j := patPointer + 1
         i := textPinter + 1
         increase textPointer by 1
      else
         return false
   done

   while j < m and pattern[j] = * symbol, do
      increase j by 1
   done

   if j = m, then
      return true
   return false
End

Example

#include<iostream>
using namespace std;

bool wildcardMatch(string text, string pattern) {
   int n = text.size();
   int m = pattern.size();

   if (m == 0)    //when pattern is empty
      return (n == 0);

   int i = 0, j = 0, textPointer = -1, pattPointer = -1;
   while (i < n) {
      if (text[i] == pattern[j]) {    //matching text and pattern characters
         i++;
         j++;
      }else if (j < m && pattern[j] == '?') {    //as ? used for one character
         i++;
         j++;
      }else if (j < m && pattern[j] == '*') {    //as * used for one or more character
         textPointer = i;
         pattPointer = j;
         j++;
      }else if (pattPointer != -1) {
         j = pattPointer + 1;
         i = textPointer + 1;
         textPointer++;
      }else
         return false;
   }

   while (j < m && pattern[j] == '*') {
      j++;     //j will increase when wildcard is *
   }

   if (j == m) {    //check whether pattern is finished or not
      return true;
   }

   return false;
}

int main() {
   string text;
   string pattern;
   cout << "Enter Text: "; cin >> text;
   cout << "Enter wildcard pattern: "; cin >> pattern;
   
   if (wildcardMatch(text, pattern))
      cout << "Pattern Matched." << endl;
   else
      cout << "Pattern is not matched" << endl;
}

Output

Enter Text: Algorithm
Enter wildcard pattern: A*it?m
Pattern Matched.

Samual Sam

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Updated on: 17-Jun-2020

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