def common_prefix(s1, s2):
if not s1 or not s2:<EOL><INDENT>return "<STR_LIT>"<EOL><DEDENT>k = <NUM_LIT:0><EOL>while s1[k] == s2[k]:<EOL><INDENT>k = k + <NUM_LIT:1><EOL>if k >= len(s1) or k >= len(s2):<EOL><INDENT>return s1[<NUM_LIT:0>:k]<EOL><DEDENT><DEDENT>return s1[<NUM_LIT:0>:k]<EOL>
Return prefix common of 2 strings