LeetCode – ReverseInteger

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231, 231 - 1], then return 0.

Assume the environment does not allow you to store 64-bit integers (signed or unsigned).

Example 1:

Input: x = 123
Output: 321

Example 2:

Input: x = -123
Output: -321

Example 3:

Input: x = 120
Output: 21

看起來很單純的題目
我第一階段的暴力解 是取餘數* 10的(長度-1)次方，每次長度都--;
結果在 大數處理的時候溢位問題很多

寫法最終如下
namespace TestProject1.Reverse_Integer;

public class ReverseInteger
{
    public int Reverse(int x)
    {
        var s = 0;
        while (x != 0)
        {
            var r = x % 10;

            var temp = s * 10 + r;

            if ((temp - r) / 10 != s) //避免溢位問題
                return 0;

            s = temp;
            x /= 10;
        }

        return s;
    }
}

using FluentAssertions;
using NUnit.Framework;
using TestProject1.Reverse_Integer;

public class ReverseIntegerTest
{
    [SetUp]
    public void Setup()
    {
    }

    [Test]
    public void Test001()
    {
        ReverseInteger ts = new ReverseInteger();
        var result = ts.Reverse(123);
        result.Should().Be(321);
    }
    
    [Test]
    public void Test002()
    {
        ReverseInteger ts = new ReverseInteger();
        var result = ts.Reverse(-123);
        result.Should().Be(-321);
    }
    
    [Test]
    public void Test003()
    {
        ReverseInteger ts = new ReverseInteger();
        var result = ts.Reverse(120);
        result.Should().Be(21);
    }  
    
    [Test]
    public void Test004()
    {
        ReverseInteger ts = new ReverseInteger();
        var result = ts.Reverse(1534236469);
        result.Should().Be(0);
    }
    
    [Test]
    public void Test005()
    {
        ReverseInteger ts = new ReverseInteger();
        var result = ts.Reverse(32768);
        result.Should().Be(86723);
    }    
    
}