7 Reverse Integer

迈不过友情╰ 2022-08-01 00:20 120阅读 0赞

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?

For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

import java.util.*;
    
    public class No7 { 
    
        public static void main(String[] args) {
    
            Scanner scanner = new Scanner(System.in);
            int input = scanner.nextInt();
            System.out.println(reverse(input));
        }
    
        public static int reverse(int x) {
            //假设的情况是输入一定不会溢出，反转后的数有可能溢出
    
            double result = 0;
    
            if (x >= Integer.MAX_VALUE || x <= Integer.MIN_VALUE) {
                return 0;
            }
    
            boolean tag = false;
            if (x < 0) {
                x = -x;
                tag = true;
            }
    
            ArrayList<Integer> arr = new ArrayList<Integer>();
    
            while (x / 10 > 0) {
    
                arr.add(x % 10);
                x = x / 10;
            }
            arr.add(x);
    
            for (int i = 0; i < arr.size(); i++) {
                result += arr.get(i) * Math.pow(10, arr.size() - 1 - i);
            }
    
            if (result >= Integer.MAX_VALUE || result <= Integer.MIN_VALUE) {
                return 0;
            }
    
            if (tag == true) {
                return (int) -result;
            } else
                return (int) result;
        }
    }