101 lines
1.8 KiB
Markdown
101 lines
1.8 KiB
Markdown
---
|
|
layout: page
|
|
title: Reverse Integer
|
|
last_solved: 2020-06-02
|
|
category: math
|
|
leetcode_url: https://leetcode.com/problems/reverse-integer
|
|
status: Solved
|
|
---
|
|
|
|
##### Problem
|
|
|
|
Given a 32-bit signed integer, reverse digits of an integer.
|
|
|
|
Example 1:
|
|
Input: 123
|
|
Output: 321
|
|
|
|
Example 2:
|
|
Input: -123
|
|
Output: -321
|
|
|
|
Example 3:
|
|
Input: 120
|
|
Output: 21
|
|
|
|
##### Solution
|
|
|
|
The tricky part of this question is handling the overflows. Check out [this](https://www.youtube.com/watch?v=ThdOYKsFSK0) video:
|
|
|
|
{% highlight python %}
|
|
|
|
def reverse(self, num: int) -> int:
|
|
|
|
# handle negative case
|
|
neg = False
|
|
if num<0:
|
|
neg = True
|
|
num = abs(num)
|
|
|
|
rev = 0
|
|
|
|
while num>0:
|
|
|
|
# pop last digit
|
|
popped = num % 10
|
|
num = math.floor(num / 10)
|
|
|
|
# handle overflow
|
|
# if (rev > 2**31 / 10) or (rev == 2**31 / 10 and popped>7): return 0
|
|
# if (rev < -2**31 / 10) or (rev == -2**31 / 10 and popped<-8): return 0
|
|
|
|
# this is good enough
|
|
if (rev >= 2**31 / 10) : return 0
|
|
if (rev <= -2**31 / 10) : return 0
|
|
|
|
rev = rev * 10 + popped
|
|
|
|
print(num, popped, rev)
|
|
|
|
|
|
return rev*-1 if neg else rev
|
|
|
|
{% endhighlight %}
|
|
|
|
|
|
```2**31 = 2147483648```
|
|
```-2**31 = -2147483648```
|
|
|
|
-2147483648 to 2147483647 Because of the range see thee last digit
|
|
|
|
This is what happens when it overflows
|
|
|
|
{% highlight text %}
|
|
153423646 9 9
|
|
15342364 6 96
|
|
1534236 4 964
|
|
153423 6 9646
|
|
15342 3 96463
|
|
1534 2 964632
|
|
153 4 9646324
|
|
15 3 96463243
|
|
1 5 964632435
|
|
0 1 9646324351
|
|
9646324351
|
|
{% endhighlight %}
|
|
|
|
This is what happens when we prevent the overflow
|
|
{% highlight text %}
|
|
153423646 9 9
|
|
15342364 6 96
|
|
1534236 4 964
|
|
153423 6 9646
|
|
15342 3 96463
|
|
1534 2 964632
|
|
153 4 9646324
|
|
15 3 96463243
|
|
1 5 964632435
|
|
0
|
|
{% endhighlight %}
|
|
|
|
![image1]() |