Match a pattern and String without using regular expressions
Given a string, find out if string follows a given pattern or not without using any regular expressions.
Input: string - GraphTreesGraph pattern - aba Output: a->Graph b->Trees Input: string - GraphGraphGraph pattern - aaa Output: a->Graph Input: string - GeeksforGeeks pattern - GfG Output: G->Geeks f->for Input: string - GeeksforGeeks pattern - GG Output: No solution exists
We can solve this problem with the help of Backtracking. For each character in the pattern, if the character is not seen before, we consider all possible sub-strings and recurse to see if it leads to the solution or not. We maintain a map that stores sub-string mapped to a pattern character. If pattern character is seen before, we use the same sub-string present in the map. If we found a solution, for each distinct character in the pattern, we print string mapped to it using our map.
Below is C++ implementation of above idea –
Time complexity of this code is O(2^m), where m is the length of the pattern. This is because in the worst case, the algorithm may have to try all possible combinations of substrings of the string to find a match with the pattern.
Space complexity is O(m), where m is the length of the pattern, as the mapping between the pattern and the string is stored in a hash map with m characters.
This article is contributed by Aditya Goel. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
Please Login to comment...