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edit_distance

Language/Type: Python recursion string return

Write a recursive function named edit_distance that accepts string parameters s1 and s2 and returns the "edit distance" between the two strings as an integer. Edit distance (also called Levenshtein distance) is defined as the minimum number of "changes" required to get from s1 to s2 or vice versa. A "change" can be defined as a) inserting a character, b) deleting a character, or c) changing a character to a different character.

Call Value Returned
edit_distance("driving", "diving") 1
edit_distance("debate", "irate") 3
edit_distance("football", "cookies") 6

Constraints: Your solution must obey the following constraints:

  • Your solution must not use any loops it must be recursive.
  • Strings have member functions named find and rfind, but you should not call them, because they allow you to get around using recursion. Similarly, the replace member is forbidden. You should limit yourself to using only the following string members:
    • at, append, compare, erase, insert, length or size, substr, trim, operators such as [], ==, !=, <, etc.
  • Do not construct any data structures (no list, set, dictionary, etc.), and do not declare any global variables. You are allowed to define other "helper" functions if you like.
Function: Write a Python function as described, not a complete program.

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