整数翻转

Question

Given a 32-bit signed integer, reverse digits of an integer.

Example 1

iput : 123
Output : 321

Example 2

Input : -123
Output : -321

Example 3

Input : 120
Output : 21

Note :
  Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [$(-2)^{31}$, $2^{31}$-1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

Answer

计算法

这是一个比较投机的方案，因为使用了数字类型long后，就不会再有溢出的问题，最后再和INT_MAX比较一下就可以了。时间复杂度为O(nlogn)

class Solution {
public:
    int reverse(int x) {
        long res = 0;
        for (;x != 0 ; x /= 10)  res = res * 10 + x % 10;
        return (res > INT_MAX || res < INT_MIN) ? 0 : res;
    }
}