module Algorithms::Search
rdoc
This module implements search algorithms. Documentation is provided for each algorithm. MIT License Copyright (c) 2009 Kanwei Li Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
Public Class Methods
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
# File lib/algorithms/search.rb, line 34 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
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
# File lib/algorithms/search.rb, line 63 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
Public Instance Methods
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
# File lib/algorithms/search.rb, line 100 def kmp_search(substring) Algorithms::Search.kmp_search(self, substring) end