Match Expression where a single special character in pattern can match one or more characters

• Difficulty Level : Easy
• Last Updated : 03 May, 2021

Given two string, in which one is a pattern (Pattern) and the other is a searching expression. Searching expression contains ‘#’.
The # works in the following way:

1. A # matches with one or more characters.
2. A # matches all characters before a pattern match is found. For example, if pat = “A#B”, and text is “ACCBB”, then # would match only with “CC” and pattern is considered as not found.

Examples :

```Input  : str = "ABABABA"
pat = "A#B#A"
Output : yes

Input  : str = "ABCCB"
pat = "A#B"
Output : yes

Input  : str = "ABCABCCE"
pat = "A#C#"
Output : yes

Input  : str = "ABCABCCE"
pat = "A#C"
Output : no```

We can observe that whenever we encounter ‘#’, we have to consider as many characters till the next character of the pattern will not be equal to the current character of the given string. Firstly, we check if the current character of the pattern is equal to ‘#’-
a) If not then we check whether the current character of string and pattern are the same or not, if same, then increment both counters else return false from here only. No need for further checking.
b) If yes, then we have to find the position of a character in the text that matches with the next character of the pattern.

C++

 `// C++ program for pattern matching``// where a single special character``// can match one more characters``#include` `using` `namespace` `std;` `// Returns true if pat matches with text``int` `regexMatch(string text, string pat)``{``    ``int` `lenText = text.length();``    ``int` `letPat = pat.length();` `    ``// i is used as an index in pattern``    ``// and j as an index in text``    ``int` `i = 0, j = 0;` `    ``// Traverse through pattern``    ``while` `(i < letPat)``    ``{``        ``// If current character of``        ``// pattern is not '#'``        ``if` `(pat[i] != ``'#'``)``        ``{``            ``// If does not match with text``            ``if` `(pat[i] != text[j])``            ``return` `false``;` `        ``// If matches, increment i and j``        ``i++;``        ``j++;``        ``}` `        ``// Current character is '#'``        ``else``        ``{``            ``// At least one character``            ``// must match with #``            ``j++;` `            ``// Match characters with # until``            ``// a matching character is found.``            ``while` `(text[j] != pat[i + 1])``            ``j++;` `            ``// Matching with # is over,``            ``// move ahead in pattern``            ``i++;``        ``}``    ``}` `    ``return` `(j == lenText);``}` `// Driver code``int` `main()``{``    ``string str = ``"ABABABA"``;``    ``string pat = ``"A#B#A"``;``    ``if` `(regexMatch(str, pat))``        ``cout << ``"yes"``;``    ``else``        ``cout << ``"no"``;``    ``return` `0;``}`

Java

 `// Java program for pattern matching``// where a single special character``// can match one more characters` `import` `java.util.*;``import` `java.lang.*;``import` `java.io.*;` `class` `GFG``{``    ``// Returns true if pat``    ``// matches with text.``    ``public` `static` `boolean` `regexMatch``                          ``(String text, String pat)``    ``{``        ``int` `lenText = text.length();``        ``int` `lenPat = pat.length();``        ` `        ``char``[] Text = text.toCharArray();``        ``char``[] Pat = pat.toCharArray();``    ` `        ``// i is used as an index in pattern``        ``// and j as an index in text.``        ``int` `i = ``0``, j = ``0``;``    ` `        ``// Traverse through pattern``        ``while` `(i < lenPat)``        ``{``            ``// If current character of``            ``// pattern is not '#'``            ``if` `(Pat[i] != ``'#'``)``            ``{``                ``// If does not match with text.``                ``if` `(Pat[i] != Text[j])``                ``return` `false``;``    ` `            ``// If matches, increment i and j``            ``i++;``            ``j++;``            ``}``    ` `            ``// Current character is '#'``            ``else``            ``{``                ``// At least one character``                ``// must match with #``                ``j++;``    ` `                ``// Match characters with # until``                ``// a matching character is found.``                ``while` `(Text[j] != Pat[i + ``1``])``                ``j++;``    ` `                ``// Matching with # is over,``                ``// move ahead in pattern``                ``i++;``            ``}``        ``}``    ` `        ``return` `(j == lenText);``    ``}` `    ``// Driver code``    ``public` `static` `void` `main (String[] args)``    ``{``        ``String str = ``"ABABABA"``;``        ``String pat = ``"A#B#A"``;``        ``if` `(regexMatch(str, pat))``            ``System.out.println(``"yes"``);``        ``else``            ``System.out.println(``"no"``);``    ``}``}` `// This code is contributed by Mr. Somesh Awasthi`

Python3

 `# Python3 program for pattern matching``# where a single special character``# can match one more characters` `# Returns true if pat matches with``# text``def` `regexMatch(text, pat):` `    ``lenText ``=` `len``(text)``    ``letPat ``=` `len``(pat)` `    ``# i is used as an index in``    ``# pattern and j as an index``    ``# in text``    ``i ``=` `0``    ``j ``=` `0` `    ``# Traverse through pattern``    ``while` `(i < letPat):` `        ``# If current character of``        ``# pattern is not '#'``        ``if` `(pat[i] !``=` `'#'``):` `            ``# If does not match with``            ``# text``            ``if` `(pat[i] !``=` `text[j]):``                ``return` `False` `            ``# If matches, increment``            ``# i and j``            ``i ``+``=` `1``            ``j ``+``=` `1` `        ``# Current character is '#'``        ``else``:` `            ``# At least one character``            ``# must match with #``            ``j ``+``=` `1` `            ``# Match characters with # until``            ``# a matching character is found.``            ``while` `(text[j] !``=` `pat[i ``+` `1``]):``                ``j ``+``=` `1` `            ``# Matching with # is over,``            ``# move ahead in pattern``            ``i ``+``=` `1` `    ``return` `(j ``=``=` `lenText)` `# Driver code``if` `__name__ ``=``=` `"__main__"``:` `    ``st ``=` `"ABABABA"``    ``pat ``=` `"A#B#A"``    ``if` `(regexMatch(st, pat)):``        ``print``(``"yes"``)``    ``else``:``        ``print``(``"no"``)` `# This code is contributed by Chitranayal`

C#

 `// C# program for pattern matching``// where a single special character``// can match one more characters``using` `System;` `class` `GFG``{``    ``// Returns true if pat``    ``// matches with text.``    ``public` `static` `bool` `regexMatch``                       ``(String text, String pat)``    ``{``        ``int` `lenText = text.Length;``        ``int` `lenPat = pat.Length;``        ` `        ``char` `[]Text = text.ToCharArray();``        ``char` `[]Pat = pat.ToCharArray();``    ` `        ``// i is used as an index in pattern``        ``// and j as an index in text.``        ``int` `i = 0, j = 0;``    ` `        ``// Traverse through pattern``        ``while` `(i < lenPat)``        ``{``            ``// If current character``            ``// of pattern is not '#'``            ``if` `(Pat[i] != ``'#'``)``            ``{``                ``// If does not match with text.``                ``if` `(Pat[i] != Text[j])``                ``return` `false``;``    ` `            ``// If matches, increment i and j``            ``i++;``            ``j++;``            ``}``    ` `            ``// Current character is '#'``            ``else``            ``{``                ``// At least one character``                ``// must match with #``                ``j++;``    ` `                ``// Match characters with # until``                ``// a matching character is found.``                ``while` `(Text[j] != Pat[i + 1])``                ``j++;``    ` `                ``// Matching with # is over,``                ``// move ahead in pattern``                ``i++;``            ``}``        ``}``    ` `        ``return` `(j == lenText);``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main ()``    ``{``        ``String str = ``"ABABABA"``;``        ``String pat = ``"A#B#A"``;``        ``if` `(regexMatch(str, pat))``            ``Console.Write(``"yes"``);``        ``else``            ``Console.Write(``"no"``);``    ``}``}` `// This code is contributed by nitin mittal`

PHP

 ``

Javascript

 ``

Output:

`yes`

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