分数加减运算

/*
 思路：
 1. 解析输入字符串，将每个分数解析出来。
 2. 使用Java Stream进行分数加法计算。
 3. 计算结果的分子和分母，并将结果转换为最简分数。
 4. 如果结果为整数，则将其转换为分数形式（分母为1）。
 */
import java.util.*;
import java.util.stream.*;
 
public class FractionAdditionStream {
    public String fractionAddition(String expression) {
        List<int[]> fractions = new ArrayList<>();
        int index = 0, n = expression.length();
        while (index < n) {
            int sign = 1;
            if (expression.charAt(index) == '-') {
                sign = -1;
                index++;
            } else if (expression.charAt(index) == '+') {
                index++;
            }
            int numerator = 0;
            while (index < n && Character.isDigit(expression.charAt(index))) {
                numerator = numerator * 10 + (expression.charAt(index) - '0');
                index++;
            }
            numerator *= sign;
            index++; // skip '/'
            int denominator = 0;
            while (index < n && Character.isDigit(expression.charAt(index))) {
                denominator = denominator * 10 + (expression.charAt(index) - '0');
                index++;
            }
            fractions.add(new int[]{numerator, denominator});
        }
        int[] result = fractions.stream()
                .reduce(new int[]{0, 1}, (a, b) -> addFractions(a[0], a[1], b[0], b[1]));
        return result[0] + "/" + result[1];
    }
 
    private int[] addFractions(int num1, int denom1, int num2, int denom2) {
        int lcm = lcm(denom1, denom2);
        int numerator = num1 * (lcm / denom1) + num2 * (lcm / denom2);
        int gcd = gcd(Math.abs(numerator), lcm);
        return new int[]{numerator / gcd, lcm / gcd};
    }
 
    private int lcm(int a, int b) {
        return a * (b / gcd(a, b));
    }
 
    private int gcd(int a, int b) {
        while (b != 0) {
            int temp = b;
            b = a % b;
            a = temp;
        }
        return a;
    }
}