Parameterized Matching Amir, Farach, Muthukrishnan Orgad Keller Modified by Ariel Rosenfeld.

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Parameterized Matching Amir, Farach, Muthukrishnan Orgad Keller Modified by Ariel Rosenfeld

Orgad Keller - Algorithms 2 - Recitation 9 2 Definition: Two strings over the alphabet, parametrized match (p-match) if the following 3 conditions apply : Parametrized Match Relation

Orgad Keller - Algorithms 2 - Recitation 9 3 Conditions

Orgad Keller - Algorithms 2 - Recitation 9 4 We can see it as a bijection : Example

Orgad Keller - Algorithms 2 - Recitation 9 5 Parametrized Matching Input: Output: All locations where p-matches.

Orgad Keller - Algorithms 2 - Recitation 9 6 Given we’ll define : In linear time… Observation

Orgad Keller - Algorithms 2 - Recitation 9 7 Now is over and is over and. We get the algorithm for p-match:  Create  Find all the places appears in (using KMP) (cond. 1+2)  Find all the places m-matches in (We’ll show later how) (cond. 3)  Return Observation

Orgad Keller - Algorithms 2 - Recitation 9 8 Why is that enough? In other words: Prove there is a p-match at location iff. (HW) We are left with the question: How do we solve step 3 efficiently? Exercise

Ariel Rosenfeld- Algorithms 2 - Recitation 9 9 M-match

Orgad Keller - Algorithms 2 - Recitation 9 10 When is the last occurrence? We’ll build an array : So, if, we know hasn’t appeared before. Otherwise, we’ll know exactly where it had appeared last. Can we do this efficiently?

Orgad Keller - Algorithms 2 - Recitation 9 11 Building the Array We’ll hold a Balanced Binary Search Tree for the symbols of the alphabet. Initially it will be empty. We’ll go over the pattern. For each symbol, if it isn’t in the tree, we’ll add it with it’s index and update. Otherwise, we know exactly where it had last appeared, so we’ll update and then update the symbol in the tree with the new index. Time: where.

Orgad Keller - Algorithms 2 - Recitation 9 12 The Matching Itself We move forward if either  and.  We’ll hold and update a balanced BST as we go over the text as well.  Time: So overall algorithm time is Can we improve this further?

Orgad Keller - Algorithms 2 - Recitation 9 13 The Trick We’ll split the text into overlapping segments of size like this:  So every match in the text must appear in whole in one of the segments. We’ll run the algorithm for each such segment. Time: where. Overall for all segments: