Completed part 2 of Day 19 puzzle with a lot of help from https://github.com/rumkugel13 to debug my code (wouldn't have finished it otherwise)

day19/day19.go

@@ -64,6 +64,7 @@ func ParseWorkflows(lines []string) map[string]Workflow {
 
 		wf = append(wf, Rule{
 			category: 'F',
+			operator: 0,
 			action:   wfLast,
 		})
 
@@ -167,3 +168,91 @@ func Part1(lines []string) int {
 
 	return sum
 }
+
+func countParts(mins Part, maxs Part) int {
+	result := 1
+
+	result *= maxs.xVal - mins.xVal + 1
+	result *= maxs.mVal - mins.mVal + 1
+	result *= maxs.aVal - mins.aVal + 1
+	result *= maxs.sVal - mins.sVal + 1
+
+	return result
+}
+
+func traverseWF(wfName string, workflows map[string]Workflow, mins Part, maxs Part) int {
+	if wfName == "R" {
+		return 0
+	}
+	if wfName == "A" {
+		return countParts(mins, maxs)
+	}
+
+	wf := workflows[wfName]
+
+	result := 0
+	for _, rule := range wf {
+		nextMins := mins
+		nextMaxs := maxs
+
+		switch rule.operator {
+		case 0:
+			result += traverseWF(rule.action, workflows, mins, maxs)
+		case '<':
+			switch rule.category {
+			case 'x':
+				nextMaxs.xVal = rule.value - 1
+				mins.xVal = rule.value
+			case 'm':
+				nextMaxs.mVal = rule.value - 1
+				mins.mVal = rule.value
+			case 'a':
+				nextMaxs.aVal = rule.value - 1
+				mins.aVal = rule.value
+			case 's':
+				nextMaxs.sVal = rule.value - 1
+				mins.sVal = rule.value
+			}
+			result += traverseWF(rule.action, workflows, nextMins, nextMaxs)
+		case '>':
+			switch rule.category {
+			case 'x':
+				nextMins.xVal = rule.value + 1
+				maxs.xVal = rule.value
+			case 'm':
+				nextMins.mVal = rule.value + 1
+				maxs.mVal = rule.value
+			case 'a':
+				nextMins.aVal = rule.value + 1
+				maxs.aVal = rule.value
+			case 's':
+				nextMins.sVal = rule.value + 1
+				maxs.sVal = rule.value
+			}
+			result += traverseWF(rule.action, workflows, nextMins, nextMaxs)
+		}
+	}
+
+	return result
+}
+
+func Part2(lines []string) int {
+	idx := 0
+	for i, line := range lines {
+		if strings.TrimSpace(line) == "" {
+			idx = i
+			break
+		}
+	}
+
+	workflows := ParseWorkflows(lines[:idx])
+
+	fmt.Println(len(workflows))
+
+	mins := Part{1, 1, 1, 1}
+	maxs := Part{4000, 4000, 4000, 4000}
+
+	result := traverseWF("in", workflows, mins, maxs)
+
+	return result
+}

day19/day19_test.go

@@ -81,3 +81,41 @@ func TestPart1WithInput(t *testing.T) {
 		t.Fatalf("expected 575412, got %d", result)
 	}
 }
+
+func TestPart2(t *testing.T) {
+	lines := []string{
+		"px{a<2006:qkq,m>2090:A,rfg}",
+		"pv{a>1716:R,A}",
+		"lnx{m>1548:A,A}",
+		"rfg{s<537:gd,x>2440:R,A}",
+		"qs{s>3448:A,lnx}",
+		"qkq{x<1416:A,crn}",
+		"crn{x>2662:A,R}",
+		"in{s<1351:px,qqz}",
+		"qqz{s>2770:qs,m<1801:hdj,R}",
+		"gd{a>3333:R,R}",
+		"hdj{m>838:A,pv}",
+		"",
+		"{x=787,m=2655,a=1222,s=2876}",
+		"{x=1679,m=44,a=2067,s=496}",
+		"{x=2036,m=264,a=79,s=2244}",
+		"{x=2461,m=1339,a=466,s=291}",
+		"{x=2127,m=1623,a=2188,s=1013}",
+	}
+
+	result := Part2(lines)
+
+	if result != 167409079868000 {
+		t.Fatalf("expected 167409079868000, got %d", result)
+	}
+}
+
+func TestPart2WithInput(t *testing.T) {
+	lines := utils.ReadLines("input.txt")
+
+	result := Part2(lines)
+
+	if result != 126107942006821 {
+		t.Fatalf("expected 126107942006821, got %d", result)
+	}
+}