Reverse Integer

2017-11-22

7. Reverse Integer

Difficulty: Easy

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

Example 1:

1 2	Input: 123 Output: 321

Example 2:

1 2	Input: -123 Output: -321

Example 3:

1 2	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.

My Solution

最简单解法，直接用系统的parseInt

class Solution {
    public int reverse(int x) {
        String ts = Math.abs(x)+"";
        StringBuilder sb=new StringBuilder();
        for(int i=ts.length()-1;i>=0;--i){
            sb.append(ts.charAt(i));
        }
        try{
            if(x<0){
                return Integer.parseInt("-"+sb.toString());
            }else{
                return Integer.parseInt(sb.toString());
            }
        }catch(Exception e){
            return 0;
        }
    }
}

取余解法

class Solution {
    public int reverse(int x) {
        long rev= 0;
        while( x != 0){
            rev= rev*10 + x % 10;
            x= x/10;
            if( rev > Integer.MAX_VALUE || rev < Integer.MIN_VALUE)
                return 0;
        }
        return (int) rev;
    }
}