Thinking of the Input
Roses are ¿red¿¿Violets are ¿blue¿¿...
Placeholder technique …
Step 1. Substitute a placeholder for the longer string
   ¿¿ û  #
Yielding
Roses are ¿red#Violets are ¿blue#
Step 2. Next, delete the shorter string
    ¿ û e
Yielding
Roses are red#Violets are blue#