1. A non-transitory computer-readable recording medium having stored therein an encoding program that causes a computer to execute a process comprising: determining whether a target character string is registered in a first dictionary, the target character string being a compression target contained in input data, the first dictionary correlating compression codes and corresponding strings; outputting a compression code corresponding to the target character string when the target string is registered in the first dictionary; searching the target character string in first data when the target character string is not registered in the first dictionary, the first date accumulating character strings that are a part of the input data and have been determined to be not registered in the first dictionary; registering a matched character string in a second dictionary different from the first dictionary when the target character string is searched in the first data; and outputting a compression code corresponding to a registration number of the target character string in the second dictionary.