分数到小数

// This solution also uses basic division and a HashMap for detecting cycles but utilizes Java Streams for formatting.
// The stream API isn't directly used here because of the nature of the problem, but we demonstrate an example with Streams for any future use case.
 
import java.util.*;
import java.util.stream.Collectors;
 
public class FractionToDecimalStream {
    public String fractionToDecimal(int numerator, int denominator) {
        if (numerator == 0) return "0";
        StringBuilder result = new StringBuilder();
        if ((numerator < 0) ^ (denominator < 0)) result.append("-");
        long num = Math.abs((long) numerator);
        long denom = Math.abs((long) denominator);
        result.append(num / denom);
        num %= denom;
        if (num == 0) return result.toString();
        result.append(".");
        Map<Long, Integer> map = new HashMap<>();
        List<Long> fractionalParts = new ArrayList<>();
        while (num != 0) {
            if (map.containsKey(num)) {
                result.insert(map.get(num), "(");
                result.append(")");
                break;
            }
            map.put(num, result.length());
            num *= 10;
            fractionalParts.add(num / denom);
            num %= denom;
        }
        result.append(fractionalParts.stream().map(String::valueOf).collect(Collectors.joining()));
        return result.toString();
    }
}