Add Edit Distance DP Algorithm

Author: turfaa

dynamic_programming/edit_distance.py

@@ -0,0 +1,74 @@
+"""
+Author  : Turfa Auliarachman
+Date    : October 12, 2016
+
+This is a pure Python implementation of Dynamic Programming solution to the edit distance problem.
+
+The problem is :
+Given two strings A and B. Find the minimum number of operations to string B such that A = B. The permitted operations are removal,  insertion, and substitution.
+"""
+
+class EditDistance:
+    """
+    Use :
+    solver              = EditDistance()
+    editDistanceResult  = solver.solve(firstString, secondString)
+    """
+
+    def __init__(self):
+        self.__prepare__()
+
+    def __prepare__(self, N = 0, M = 0):
+        self.dp = [[-1 for y in range(0,M)] for x in range(0,N)]
+
+    def __solveDP(self, x, y):
+        if (x==-1):
+            return y+1
+        elif (y==-1):
+            return x+1
+        elif (self.dp[x][y]>-1):
+            return self.dp[x][y]
+        else:
+            if (self.A[x]==self.B[y]):
+                self.dp[x][y] = self.__solveDP(x-1,y-1)
+            else:
+                self.dp[x][y] = 1+min(self.__solveDP(x,y-1), self.__solveDP(x-1,y), self.__solveDP(x-1,y-1))
+
+            return self.dp[x][y]
+
+    def solve(self, A, B):
+        if isinstance(A,bytes):
+            A = A.decode('ascii')
+
+        if isinstance(B,bytes):
+            B = B.decode('ascii')
+
+        self.A = str(A)
+        self.B = str(B)
+
+        self.__prepare__(len(A), len(B))
+
+        return self.__solveDP(len(A)-1, len(B)-1)
+
+if __name__ == '__main__':
+        import sys
+        if sys.version_info.major < 3:
+            input_function = raw_input
+        else:
+            input_function = input
+
+        solver = EditDistance()
+
+        print("****************** Testing Edit Distance DP Algorithm ******************")
+        print()
+
+        print("Enter the first string: ", end="")
+        S1 = input_function()
+
+        print("Enter the second string: ", end="")
+        S2 = input_function()
+
+        print()
+        print("The minimum Edit Distance is: %d" % (solver.solve(S1, S2)))
+        print()
+        print("*************** End of Testing Edit Distance DP Algorithm ***************")