leetcode — reverse-integer

/**
* Source : https://oj.leetcode.com/problems/reverse-integer/ *
* Created by lverpeng on 2017/7/4.
*
* Reverse digits of an integer.
*
* Example1: x =  123, return  321
* Example2: x = -123, return -321
*
*
* 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).
*
*/
public class ReverseInteger {

/**
* 翻转一个int类型的数，几种特殊情况考虑
* 1. 末尾是零的处理方式：去掉
* 2. 溢出：一种方式注解返回0，一种是当做无符号int输出
*
* 从右至左取出每一位数，然后组成新的数
* 取余，整除的方法
*
* @param num
* @return
*/
public int reverse (int num) {
int temp = 0;
int result = 0;
while (num != 0) {
// 判断溢出
if (result > Integer.MAX_VALUE / 10 || result < Integer.MIN_VALUE / 10) {
// 溢出返回0
return 0;
}
// 最后一位数
temp = num % 10;
result = result * 10 + temp;
// 去除最后一位
num = num / 10;
}
return result;
}

/**
* 溢出不返回0，返回翻转后的数，使用long表示
* @param num
* @return
*/
public long reverse1 (int num) {
int temp = 0;
long result = 0;
while (num != 0) {
// 最后一位数
temp = num % 10;
result = result * 10 + temp;
// 去除最后一位
num = num / 10;
}
return result;
}

public static void main(String[] args) {
ReverseInteger reverseInteger = new ReverseInteger();
System.out.println(reverseInteger.reverse(123) + " === " + "321");
System.out.println(reverseInteger.reverse(-123) + " === " + "-321");
System.out.println(reverseInteger.reverse(-100) + " === " + "-1");
System.out.println(reverseInteger.reverse(1002) + " === " + "2001");
System.out.println(reverseInteger.reverse(123) + " === " + "321");

System.out.println(reverseInteger.reverse(1463847412) + " === " + "2147483641");
System.out.println(reverseInteger.reverse(2147447412) + " === " + "2147447412");
System.out.println(reverseInteger.reverse(2147447412) + " === " + "2147447412");

// overfow
System.out.println(reverseInteger.reverse(1000000003) + " === " + "0");
System.out.println(reverseInteger.reverse(2147483647) + " === " + "0");
System.out.println(reverseInteger.reverse(-2147483648) + " === " + "0");

System.out.println("");
System.out.println("-------------");
System.out.println("");

//
System.out.println(reverseInteger.reverse1(123) + " === " + "321");
System.out.println(reverseInteger.reverse1(-123) + " === " + "-321");
System.out.println(reverseInteger.reverse1(-100) + " === " + "-1");
System.out.println(reverseInteger.reverse1(1002) + " === " + "2001");
System.out.println(reverseInteger.reverse1(123) + " === " + "321");

//
System.out.println(reverseInteger.reverse1(1463847412) + " === " + "2147483641");
System.out.println(reverseInteger.reverse1(2147447412) + " === " + "2147447412");
System.out.println(reverseInteger.reverse1(2147447412) + " === " + "2147447412");

// overflow
System.out.println(reverseInteger.reverse1(1000000003) + " === " + "3000000001");
System.out.println(reverseInteger.reverse1(2147483647) + " === " + "7463847412");
System.out.println(reverseInteger.reverse1(-2147483648) + " === " + "-8463847412");
}
}