1. A processor-executed method of integrating an existing source code into a target source code, the method comprising: mapping a plurality of candidate mappings between a change point of the existing source code and a plurality of change points of the target source code; selecting a candidate mapping of the plurality of candidate mappings; forming a plurality of change point pairs by pairing the change point of the existing source code with each change point of the plurality of change points of the target source code; selecting the plurality of suggested candidate mappings from the plurality of change point pairs; filtering a number of available change point pairs to be selected from, based on a previously selected candidate mapping; automatically updating the existing source code based on the candidate mapping having been selected, using a processor on a computer; and transplanting the existing source code having been updated into the target source code.