rotate_for_a_max.r

# Let us begin with an example:

# Take a number: 56789. Rotate left, you get 67895.

# Keep the first digit in place and rotate left the other digits: 68957.

# Keep the first two digits in place and rotate the other ones: 68579.

# Keep the first three digits and rotate left the rest: 68597. Now it is over since keeping the first
# four it remains only one digit which rotated is itself.

# You have the following sequence of numbers:

# 56789 -> 67895 -> 68957 -> 68579 -> 68597

# and you must return the greatest: 68957.

# Task
# Write function max_rot(n) which given a positive integer n returns the maximum number you got doing
# rotations similar to the above example.

# So max_rot (or maxRot or ... depending on the language) is such as:

# max_rot(56789) should return 68957

# max_rot(38458215) should return 85821534

vectorToNumber <- function(v) {
  num <- 0
  i <- 1
  k <- length(v)-1
  while (k >= 0) {
    num <- num + (v[i] * 10^k)
    k <- k - 1
    i <- i + 1
  }
  
  return(num)
}

maxRot <- function(n) {
  number <- as.numeric(strsplit(as.character(n), "")[[1]])
  
  i <- 1
  greatest <- vectorToNumber(number)
  
  while (i < length(number)) {
    number <- c(number, number[i])[-i]
    buffer <- vectorToNumber(number)
    if (buffer > greatest) {
      greatest <- buffer
    }
    i <- i + 1
    if (number[i+1] < number[i]) {
      break
    }
  }
  
  return(greatest)
  
}