A couple is putting up the Christmas tree. The boy loves Christmas decorations and wants it to be perfectly balanced. He has three types of decorations:

  • Colored balls: B
  • Small gifts: R
  • Pine cones: P

The Christmas tree is a triangle that must be generated. They already have the base mounted, which would be the first row, and from there they have to place the decorations upwards following a formula.

Place on top :    P     R     B     P
If below is  :   P P   B P   R P   B R

The combinations are also reversed. For example, if below is B P, above is R. But it will also be R if below is P B. Also if below you have repeated the letter, above you use the same letter. For example: if below is B B, above is B.

With these rules, we could see the tree that we would generate with the base B P R P:

  P B
 R B B

Write a program that receives the string B P R P and returns an array with the representation of the tree.

decorateTree('B P R P')
// [
// 'R',
// 'P B',
// 'R B B',
// 'B P R P'
// ]

decorateTree('B B') // ['B', 'B B']

Keep in mind that:

  • The program always receives the text string that represents the base of the tree.
  • The tree must be generated completely, that is, the base and the rows that are generated from it, until the top.
  • You have to follow the formula to know which decoration to place in each position.