// LeetCode 166: Fraction To Recurring Decimal
// 難度: Medium
// 日期: 2025-09-24

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class Solution
{
    public string FractionToDecimal(int numerator, int denominator)
    {
        if (numerator == 0) return "0";

        long num = numerator;
        long den = denominator;

        StringBuilder result = new StringBuilder();
        bool isNegative = (num < 0) ^ (den < 0);
        if (isNegative) result.Append('-');

        num = Math.Abs(num);
        den = Math.Abs(den);

        long integerPart = num / den;
        result.Append(integerPart);

        long remainder = num % den;
        if (remainder == 0) return result.ToString();

        result.Append('.');
        result.Append(CalculateDecimalPart(remainder, den));

        return result.ToString();
    }

    private string CalculateDecimalPart(long remainder, long denominator)
    {
        StringBuilder decimalBuilder = new StringBuilder();
        Dictionary<long, int> remainderMap = new Dictionary<long, int>();

        while (remainder != 0)
        {
            if (remainderMap.TryGetValue(remainder, out int repeatIndex))
            {
                decimalBuilder.Insert(repeatIndex, '(');
                decimalBuilder.Append(')');
                break;
            }

            remainderMap[remainder] = decimalBuilder.Length;
            remainder *= 10;
            long digit = remainder / denominator;
            decimalBuilder.Append(digit);
            remainder %= denominator;
        }

        return decimalBuilder.ToString();
    }
}

public class Program {
    public static void Main() {
        var s = new Solution();
        
    }
}