Reverse integer is another interview question, that allegedly could be asked by the interviewer. Original question or problem is posted at the Leetcode.

The problem is described as:

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-2^31, 2^31 – 1], then return 0.

For example:

x = 120; reversed_x = 21
x = -2310; reversed_x = -132

Useless function kind of looks cool.

reverseInteger <- function(x){
  if ( -2**31 < x & x > 2**31 -1) return(0) #must be inside the integer boundaries
  if (x < 0) { 
    x2 <- x*-1
    r_ints <- (rev(strsplit(as.character(x2), "")[[1]]))
  } else {
    r_ints <- (rev(strsplit(as.character(x), "")[[1]]))
  }
  r_ints2 <- paste(r_ints, collapse = "")
  r_ints2 <- as.numeric(r_ints2)
  
  return(r_ints2)
}

And we run the some normal numbers to test the validity:

reverseInteger(-4122310)
# [1] -132214
reverseInteger(122310)
# [1] 13221
reverseInteger(12223456789)
# [1] 0

So it looks. Right, all good. What if we take the edge case of 2147483647 (which is 2^31-1). When we reverse the number, we get 7463847412, making the solution fall out of the boundaries of an integer with the size of 2^31, even though the original number still falls within the boundaries.

In this case, we add additional checker:

reverseInteger <- function(x){
  if ( -2**31 < x & x > 2**31 -1) return(0) #must be inside the integer boundaries
  if (x < 0) { 
    x2 <- x*-1
    r_ints <- (rev(strsplit(as.character(x2), "")[[1]]))
  } else {
    r_ints <- (rev(strsplit(as.character(x), "")[[1]]))
  }
  r_ints2 <- paste(r_ints, collapse = "")
  r_ints2 <- as.numeric(r_ints2)
  

  if ( -2**31 < r_ints2 & r_ints2 > 2**31 -1) {
      return(0) 
  } else {
  return(r_ints2)
 }
}
}

And now we can test the function against the bigger number:

reverseInteger(2147483646)
# [1] 0

As always, code is available on Github in  Useless_R_function repository. The sample file in this repository is called: ReverseInteger.R. Check the repository for future updates.

Happy R-coding and stay healthy!