The Diff Match and Patch libraries offer robust algorithms to perform the
operations required for synchronizing plain text.

Diff: Compare two blocks of plain text and efficiently return a list of
differences.

Match: Given a search string, find its best fuzzy match in a block of plain
text. Weighted for both accuracy and location.

Patch: Apply a list of patches onto plain text. Use best-effort to apply patch
even when the underlying text doesn't match.

WWW: https://code.google.com/p/google-diff-match-patch/