Problem:
Score : 300 points

Problem Statement

You are given a string S consisting of lowercase English letters.
Another string T is initially empty.
Determine whether it is possible to obtain S = T by performing the following operation an arbitrary number of times:

Append one of the following at the end of T: dream, dreamer, erase and eraser.

Constraints

1≦|S|≦10^5

S consists of lowercase English letters.

Input

The input is given from Standard Input in the following format:

S

Output

If it is possible to obtain S = T, print YES. Otherwise, print NO.

Sample Input 1

erasedream

Sample Output 1

YES

Append erase and dream at the end of T in this order, to obtain S = T.

Sample Input 2

dreameraser

Sample Output 2

YES

Append dream and eraser at the end of T in this order, to obtain S = T.

Sample Input 3

dreamerer

Sample Output 3

NO

Solution in Scala (2.11.7) (judge verdict: Accepted)

import java.io.{BufferedOutputStream, BufferedReader, InputStreamReader, PrintWriter}

import scala.annotation.tailrec

object Main {
  def main(args: Array[String]): Unit = {
    val in = new BufferedReader(new InputStreamReader(System.in))
    val out = new PrintWriter(new BufferedOutputStream(System.out))
    val s = in.readLine()

    val candidates = List("dream", "dreamer", "erase", "eraser")

    @tailrec
    def isMatch(ss: List[String]): Boolean = {
      ss match {
        case Nil => false
        case s :: rest =>
          if (s == "") {
            true
          } else {
            isMatch(
              rest ++ candidates.collect {
                case candidate: String if s.startsWith(candidate) =>
                  s.substring(candidate.length)
              }
            )
          }
      }
    }

    out.println(
      if (isMatch(List(s))) {
        "YES"
      } else {
        "NO"
      }
    )
    out.flush()
  }
}