Query Optimization - To repeat a pattern in Oracle SQL

Question

Here is my Code:

SELECT A.*, (CASE WHEN A.r = 1 then \'X1\' when A.r = 2 then \'X2\' when A.r = 3 then \'X3\' when A.r = 4 
then \'X4\' when A.r = 5 then \'X2