Module: Algorithms::Search
- Defined in:
- lib/algorithms/search.rb
Overview
This module implements search algorithms. Documentation is provided for each algorithm.
Class Method Summary collapse
-
.binary_search(container, item) ⇒ Object
Binary Search: This search finds an item in log(n) time provided that the container is already sorted.
-
.kmp_search(string, substring) ⇒ Object
Knuth-Morris-Pratt Algorithm substring search algorithm: Efficiently finds the starting position of a substring in a string.
Instance Method Summary collapse
-
#kmp_search(substring) ⇒ Object
Allows kmp_search to be called as an instance method in classes that include the Search module.
Class Method Details
.binary_search(container, item) ⇒ Object
Binary Search: This search finds an item in log(n) time provided that the container is already sorted. The method returns the item if it is found, or nil if it is not. If there are duplicates, the first one found is returned, and this is not guaranteed to be the smallest or largest item.
Complexity: O(lg N)
Algorithms::Search.binary_search([1, 2, 3], 1) #=> 1
Algorithms::Search.binary_search([1, 2, 3], 4) #=> nil
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# File 'lib/algorithms/search.rb', line 14 def self.binary_search(container, item) return nil if item.nil? low = 0 high = container.size - 1 while low <= high mid = (low + high) / 2 val = container[mid] if val > item high = mid - 1 elsif val < item low = mid + 1 else return val end end nil end |
.kmp_search(string, substring) ⇒ Object
Knuth-Morris-Pratt Algorithm substring search algorithm: Efficiently finds the starting position of a substring in a string. The algorithm calculates the best position to resume searching from if a failure occurs.
The method returns the index of the starting position in the string where the substring is found. If there is no match, nil is returned.
Complexity: O(n + k), where n is the length of the string and k is the length of the substring.
Algorithms::Search.kmp_search("ABC ABCDAB ABCDABCDABDE", "ABCDABD") #=> 15
Algorithms::Search.kmp_search("ABC ABCDAB ABCDABCDABDE", "ABCDEF") #=> nil
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# File 'lib/algorithms/search.rb', line 43 def self.kmp_search(string, substring) return nil if string.nil? or substring.nil? # create failure function table pos = 2 cnd = 0 failure_table = [-1, 0] while pos < substring.length if substring[pos - 1] == substring[cnd] failure_table[pos] = cnd + 1 pos += 1 cnd += 1 elsif cnd > 0 cnd = failure_table[cnd] else failure_table[pos] = 0 pos += 1 end end m = i = 0 while m + i < string.length if substring[i] == string[m + i] i += 1 return m if i == substring.length else m = m + i - failure_table[i] i = failure_table[i] if i > 0 end end return nil end |
Instance Method Details
#kmp_search(substring) ⇒ Object
Allows kmp_search to be called as an instance method in classes that include the Search module.
class String; include Algorithms::Search; end
"ABC ABCDAB ABCDABCDABDE".kmp_search("ABCDABD") #=> 15
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# File 'lib/algorithms/search.rb', line 80 def kmp_search(substring) Algorithms::Search.kmp_search(self, substring) end |