solution-m5/003

projects/003-string-edit-distance/python/main.py

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+'''
+The edit distance between two strings is a measure of their similarity. 
+
+The smaller the edit distance, the more similar the strings are with regard to the minimum number of insert,
+delete and substitute operations needed to transform one string into the other.   
+
+Consider the strings kitten and sitting.  
+The first string can be transformed into the second string with the following operations: 
+Substitute the k with an s, substitute the e with an i, and insert a g at the end of the string.   
+This is the smallest number of operations that can be performed to transform kitten into sitting.
+
+As a result, the edit distance is 3.
+
+Write a recursive function that computes the edit distance between two strings.
+
+Use the following algorithm:
+
+    Let s and t be the strings 
+
+        If the length of s is 0 then
+            Return the length of t
+
+        Else if the length of t is 0 then
+            Return the length of s 
+
+        Else 
+        Set cost to 0
+
+        If the last character in s does not equal the last character in t then
+
+            Set cost to 1
+            Set d1 equal to the edit distance between all characters except the last one
+                in s, and all characters in t, plus 1
+            Set d2 equal to the edit distance between all characters in s, and all
+                characters except the last one in t, plus 1
+            Set d3 equal to the edit distance between all characters except the last one
+                in s, and all characters except the last one in t, plus cost Return the minimum of d1, d2 and d3
+
+
+
+Use your recursive function to write a program that reads two strings from the user and displays the edit distance between them.
+'''
+
+def editdistance(s, t):
+    if len(s) == 0:
+        return len(t)
+    elif len(t) == 0:
+        return len(s) 
+    else:
+        cost = 0
+
+    if s[-1] != t[-1]:
+        cost = 1
+
+    d1 = editdistance(s[:-1], t) + 1
+    d2 = editdistance(s, t[:-1]) + 1
+    d3 = editdistance(s[:-1], t[:-1]) + cost
+
+    return min(d1, d2, d3)
+
+def main():
+    s = input("Please input first string: ")
+    t = input("Please input second string: ")
+    x = editdistance(s, t)
+    print(x)
+
+if __name__ == '__main__':
+    main()