For our first assignment in Learning Machines, Patrick asked us to implement run-length encoding in Python.
Below is my code, which includes encode and decode functions.
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def encode(u): # init tracking vars enc = list() cur = list(u[0]) # iterate through string for i in range(1, len(u)): if u[i] == u[i-1]: cur.append(u[i]) else: enc.append((len(cur), u[i-1])) cur = list(u[i]) # handle last character enc.append((len(cur), cur[0])) def rep(tup): # encode using backtick as delimeter count, char = tup if count == 1: return char else: return "%s`%i`" % (char, count) return ''.join(map(rep, enc)) def decode(e): # init tracking vars result = list() cur_num = list() # switch var on_num = False # iterate through encoded string for i, char in enumerate(e): # if delimeter found... if char == "`": # switch on/off on_num = not on_num # if closing delimeter if not on_num: result.append( rep_char*int(''.join(cur_num)) ) cur_num = list() # if opening delimeter elif on_num and i > 0: # repeated char is last # added to result rep_char = result.pop() # if not delimeter and not on number elif not on_num: result.append(char) # if not delimeter and on number else: cur_num.append(char) return ''.join(result) if __name__ == '__main__': import sys to_encode = sys.argv[1] encoded = encode(to_encode) decoded = decode(encoded) print encoded print decoded assert to_encode == decoded |
