Reverse a integer @ Leetcode

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Reverse digits of an integer.

Example1: x = 123, return 321
Example2: x = -123, return -321

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Have you thought about this?

Here are some good questions to ask before coding. Bonus points for you if you have already thought through this!

If the integer's last digit is 0, what should the output be? ie, cases such as 10, 100.

Did you notice that the reversed integer might overflow? Assume the input is a 32-bit integer, then the reverse of 1000000003 overflows. How should you handle such cases?

Throw an exception? Good, but what if throwing an exception is not an option? You would then have to re-design the function (ie, add an extra parameter).

In the very first, I thought to convert the integer to string, then the problem transferred to reverse the string which is familiar to most people. However, we need to consider the problem that, the integer may be ended with 0. In this case, we need to filter the 0 and only keep the digits greater than 0. BUT!!! we have to keep in mind is, a string is a const variable which can not be modified once it is given a value. So if we want to use the string, we may need to copy the digits->chars to a new string which makes problem much more tedious and complicate. Why not change our mind to another way? Yes! We can make problem simple by only adding the digits one by one through end to begin. That's it! Oh, keep in mind there may be overflow after the reverse. If in this place, just return -1.

That's my code. At the first, I set a bool variable to see whether x is positive or not. Actually it's not necessary.

Some basic knowledge I have learnt from this problem:

Convert a integer to a string, we can use
char * itoa(int x, char * str, int base) while this is not a function in library, so it's not wise to use it. We may also use
 std:: stringstream ss;
 ss << number;
 string result = ss.str();

There is a std:: to_string() in c++11 that we can use directly.