7. Reverse Integer

問題

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

Note:
Assume we are dealing with an environment which could only hold integers within the 32-bit signed integer range. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

分析：

將數字翻轉，如果超過32-bit就返回0.

照常翻轉就可以，定義的res爲int 32-bit，如果翻轉後超出範圍，那必然每一位會發生很大的變化。根據這個特性可以在迭代生成output時檢查是否有突變，若突變則返回0.

java

class Solution {
    public int reverse(int x) {
        int res = 0, privious = 0;
        while(x != 0){
            privious = res;
            res = res * 10 + (x%10);
            if(res/10 != privious) return 0; //檢查突變
            x /= 10;
        }
        return res;
    }
}