Reverse Integer

题目描述

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.

翻转整数，如果越界了就返回 0。

解题思路

转换成字符串，用 long 存储检查大小。

代码

class Solution {
    public int reverse(int x) {
        String tmp = String.valueOf(x);
        long ret = 0;
        for (int i = tmp.length()-1; i >= 0; i--) {
            if (i == 0 && tmp.charAt(i) == '-') {
                ret *= -1;
            } else if (i == 0 && tmp.charAt(i) == '+') {
                break;
            } else if (tmp.charAt(i) >= '0' && tmp.charAt(i) <= '9') {
                ret *= 10;
                ret = ret + tmp.charAt(i) - '0';
            } else {
                return 0;
            }
        }
        if (ret > Integer.MAX_VALUE || ret < Integer.MIN_VALUE)
            return 0;
        return (int)ret;
    }
}