Fraction Addition and Subtraction

Problem

Given a string representing an expression of fraction addition and subtraction, you need to return the calculation result in string format. The final result should be irreducible fraction. If your final result is an integer, say 2, you need to change it to the format of fraction that has denominator 1. So in this case, 2 should be converted to 2/1.

Example 1:
Input:"-1/2+1/2"
Output: "0/1"
Example 2:
Input:"-1/2+1/2+1/3"
Output: "1/3"
Example 3:
Input:"1/3-1/2"
Output: "-1/6"
Example 4:
Input:"5/3+1/3"
Output: "2/1"

Note:

• The input string only contains '0' to '9', '/', '+' and '-'. So does the output.
• Each fraction (input and output) has format ±numerator/denominator. If the first input fraction or the output is positive, then '+' will be omitted.
• The input only contains valid irreducible fractions, where the numerator and denominator of each fraction will always be in the range [1,10]. If the denominator is 1, it means this fraction is actually an integer in a fraction format defined above.
• The number of given fractions will be in the range [1,10].
• The numerator and denominator of the final result are guaranteed to be valid and in the range of 32-bit int.

Solution

public class Solution {
    public String fractionAddition(String expression) {
        //Get each fraction from the given expression
        String[] fracts = expression.split("(?=[+,-])");
        String res = "0/1";
        //Add every two fraction using helper method add()
        for (String fract : fracts) res = add(res, fract);
        return res;
    }

    private String add(String f1, String f2) {
        //Get numerator and denominator from String to String[] and convert to int[]
        int[] n1 = Stream.of(f1.split("/")).mapToInt(Integer::parseInt).toArray();
        int[] n2 = Stream.of(f2.split("/")).mapToInt(Integer::parseInt).toArray();
        int numer = n1[0] * n2[1] + n2[0] * n1[1]; 
        int denmo = n1[1] * n2[1];
        //Get greatest common divisor to simplify the result fraction
        int gcd = Math.abs(getGcd(numer, denmo));
        return numer / gcd + "/" + denmo / gcd;
    }

    private int getGcd(int a, int b) {
        return a == 0 || b == 0 ? a + b : getGcd(b, a % b);
    }
}

Analysis

Each steps are written well in the comments above
The tricky part of this problem is to simplify the fraction
We use gcd to simplify both numerator and denominator
Also notice how we use regex and convert different type of vars in this solution