Leetcode#7 Reverse Integer

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leetcode solutions (through java)

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).

Solution:

变化前后对比——用一个变量存储变化后的值，每次做反向操作，如果和之前的值一样就更新，不一样，说明溢出。

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class Solution {
    public int reverse(int x){
        boolean tag =false;
        int result=0;
        int newres=0;
        if(x<0){
            x = -x;
            tag = true;
        }
        while(x!=0){
            newres=result*10+x%10;
            if((newres-x%10)/10!=result){
                return 0;
            }//不等，说明溢出
            result=newres;
            x /= 10;
        }
        if(tag){
            return -result;
        }
        return result;
    }
}