Adding implementation of editdistance

Author: ApsaraGuhan

dynamic_programming/editdistance.rb

@@ -0,0 +1,74 @@
+require "test/unit"
+
+def editDistDP(str1, str2, m, n) 
+    rows, cols = m+1,n+1  
+
+    # Create a 2D array to store results of subproblems
+    dp = Array.new(rows) { Array.new(cols) }
+
+    #using bottom up approach
+    for i in (0..m + 1-1) do
+        for j in (0..n + 1-1) do
+
+            #If the first string is empty, insert all the characters of the second string
+            if i == 0 
+                dp[i][j] = j   
+        
+            #If the second string is empty, insert all the characters of the first string
+            elsif j == 0 
+                dp[i][j]  = i 
+            
+            #If the last character in both the strings are same, we can ignore the character and move to the next character in both the strings
+            elsif str1[i-1] == str2[j-1] 
+                dp[i][j] =  dp[i-1][j-1] 
+            
+            #If the last character of both the strings are different, find out the minimum value of the three operations(insert, delete, replace)
+            else
+                dp[i][j] = 1 +[dp[i][j-1],dp[i-1][j],dp[i-1][j-1]].min()
+                
+            end
+        
+        end
+        
+    end
+    
+    return dp[m][n]
+end
+
+
+
+
+class Editdistancetest < Test::Unit::TestCase
+    
+    #Test1
+    #Replace 'n' with 'r'
+    #insert 'a'
+    #insert 't'
+    #No of total operations : 3
+    def test_distance1
+      assert_equal 3, editDistDP( "sunday","saturday",6,8), "Should return 3" 
+    end
+  
+    #Test2
+    #Replace 'a' with 'u'
+    #No of total operations : 1
+    def test_distance2
+      assert_equal 1, editDistDP("cat","cut",3,3), "editDistDpShould return 1"
+    end
+
+    #Test3
+    #Insert 'a','p', 'p','l','e','p','i','e' into string 1
+    #No of total operations : 8
+    def test_distance3
+       assert_equal 8, editDistDP("","applepie",0,8), "editDistDpShould return 1"
+    end
+
+    #Test4
+    #Both the strings are equal, thus no operation needed
+    #No of total operations : 0
+    def test_distance4
+       assert_equal 0, editDistDP("Hello","Hello",5,5), "editDistDpShould return 1" 
+    end
+
+  end
+