I get the basic gist of edit distance, but there's a part in one of the walkthrough videos for pset6/similarities which I don't understand.
He's trying to figure out the edit distance from converting 'C' to 'A'. First he looks one square from the top (i.e. going from ' ' to 'A') which is 1,I.
Then using 1,I he computes 'C' to 'A' with 2,D.
But question is, how is the last operation a D?
If you go from ' ' to 'A', which is 1,I, and then 'A' to 'C', then wouldn't the computation be 2,S with the last operation being a substituion (of 'A' into 'C') instead of a deletion?
Please help me understand how this is a deletion instead of a substitution.