Problem 7.Reverse digits of an integer.

Problem 7.Reverse digits of an integer.

Example1: x = 123, return 321
Example2: x = -123, return -321。 —— [leetcode Problem 7 ]

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?

For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

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此题需要注意越界的情况，int类型大多数编译器中为32位，最高位是符号位，剩下31位表示数值，可用0x7fffffff表示最大值，更好的方式使用limits.h中的INT_MAX。如果使用unsigned int 定义res,也会出现溢出，因为unsigned int 范围最大为0xffffffff=4294967295，会出现Input: 1534236469 Output: 1056389759 Expected: 0的不正确结果

class Solution {public:    int reverse(int x) {        bool sign=true;        if(x<0)            sign=false,x=-x;        unsigned long long res=0;        while(x){            res=res*10+x%10;            x=x/10;        }        if(res>INT_MAX)            return 0;        if(sign)            return res;        else            return (int)-res;    }};