Added KMP implementation in Ruby (jainaman224#2555) (jainaman224#2848)

Knuth_Morris_Pratt_Algorithm/KMP.rb

@@ -0,0 +1,76 @@
+# Given a text and a pattern, we need to find all occurrences of pattern in text
+
+def kmp_search(pattern, text)
+    pattern_size = pattern.length
+    text_size = text.length
+
+    lps = Array.new(pattern_size) # longest_prefix_suffix array 
+    lps = calculate_lps(pattern, lps) # compute lps[]
+    i = 0 # index for pattern[]
+    j = 0 # index for text[]
+
+    while i < text_size
+        if pattern[j] == text[i]
+            i += 1
+            j += 1
+        end
+
+        if j == pattern_size
+            puts "Pattern found at #{i - j + 1}"
+            j = lps[j - 1]
+        elsif i < text_size && pattern[j] != text[i]
+            if j != 0
+                j = lps[j - 1]
+            else
+                i += 1
+            end
+        end
+    end
+end
+
+# function to preprocess lps[] to hold the longest prefix suffix values for pattern
+def calculate_lps(pattern, lps)
+    len = 0
+    lps[0] = 0
+
+    i = 1
+    while i < pattern.length
+        if pattern[i] == pattern[len]
+            len += 1
+            lps[i] = len
+            i += 1
+        else
+            if len != 0
+                len = lps[len - 1]
+            else
+                lps[i] = 0
+                i += 1
+            end
+        end
+    end
+
+    return lps
+end
+
+# Driver Code
+puts "Enter the text:"
+text = gets.chomp
+
+puts "Enter the pattern:"
+pattern = gets.chomp
+
+kmp_search(pattern, text)
+
+=begin
+Enter the text:
+namanchamanbomanamansanam
+
+Enter the pattern:
+aman
+
+Output
+
+Pattern found at 2
+Pattern found at 8
+Pattern found at 17
+=end