Two strings are k-bonded if they share at least k common characters. Each character can contribute at most one bond. For instance, “aabbccddXYZABeeffGg” and “Gfeeexyzab” are 1-, 2-, 3-, 4-, 5- and 6-bonded. Define function IsBonded(k, s1, s2), returning true iff s1 and s2 are k-bonded.