This is the first in a series of posts dissecting typical coding interview questions. I will begin with a pretty simple one - reversing an integer.

def reverse_int(n):
  rev = 0
  while num > 0: # n < 10 / 10 = 0
    rev = rev * 10 # shift current rev to left to append digit
    rev = rev + (num % 10) # get last digit of num
    num = num / 10 # chop off last digit of num

Tracing a Call

reverse_int(492)

1. Loop 1
   1. rev is 0
   2. rev is rev * 10 = 0
   3. rev is rev + (num % 10) = 2
   4. num = 49
2. Loop 2
   1. revis rev * 10 = 20
   2. rev is rev + (num % 10) = 29
   3. num = 4
3. Loop 3
   1. rev = rev * 10 = 290
   2. rev = rev + (num % 10) = 294
   3. num = 0