ReverseInteger
Problem
Solution
Extract the sign of x. We can use modulus and division to get the digits of
x. Reverse the list of digits. Then check that the digits are in the range
\([2^{31} - 1, -2^{31}]\). If so, calculate the reversed integer using
the expansion
\[r = \sum_{i=0}^{n-1} 10^i d_i.\]
Code
https://github.com/GeorgeRPu/tech-interview-prep/blob/main/solutions/ReverseInteger.py
>>> reverse(-123)
-321
>>> reverse(120)
21
"""
def reverse(x: int) -> int:
sign = 1 if x > 0 else -1
x = sign * x
digits = []
while x > 0:
remainder = x % 10
digits.append(remainder)
x = x // 10
digits = digits[::-1]
if too_large(sign, digits):
return 0
else:
r = 0
for i, digit in enumerate(digits):
r += digit * 10**i
return sign * r
def too_large(sign, digits):
if len(digits) < 10:
return False
if len(digits) > 10:
return True
tl = False
limit = 2**31 - 1 if sign == 1 else 2**31
for digit in enumerate(digits):
limit_digit = limit % 10
if digit > limit_digit:
tl = True
elif digit < limit_digit:
tl = False
limit = limit // 10
return tl
Test
>>> from ReverseInteger import reverse
>>> reverse(123)
321
>>> reverse(-123)
-321
>>> reverse(120)
21
Functions
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