go: add «592. Fraction Addition and Subtraction»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/fraction-addition-and-subtraction.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+)
+
+func fractionAddition(expression string) string {
+	abs := func(x int) int {
+		return max(-x, x)
+	}
+	gcd := func(x, y int) int {
+		for y != 0 {
+			x, y = y, x%y
+		}
+		return x
+	}
+	NUM_REGEX, _ := regexp.Compile("[+-]?[0-9]+")
+
+	num, denom := 0, 1
+
+	nums := NUM_REGEX.FindAllString(expression, -1)
+	for i := 0; i < len(nums); i += 2 {
+		next_num, ok := strconv.Atoi(nums[i])
+		if ok != nil {
+			panic("failed to parse numerator")
+		}
+
+		next_denom, ok := strconv.Atoi(nums[i+1])
+		if ok != nil {
+			panic("failed to parse denominator")
+		}
+
+		num = num*next_denom + next_num*denom
+		denom *= next_denom
+	}
+
+	d := abs(gcd(num, denom))
+
+	num /= d
+	denom /= d
+
+	return fmt.Sprintf("%d/%d", num, denom)
+}