Add solution for day 3

main.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"unsupervised.ca/aoc2021/one"
+	"unsupervised.ca/aoc2021/three"
 	"unsupervised.ca/aoc2021/two"
 )
 
@@ -28,6 +29,8 @@ func main() {
 		day = one.Init("one/input.txt")
 	case "two":
 		day = two.Init("two/input.txt")
+	case "three":
+		day = three.Init("three/input.txt")
 	default:
 		fmt.Printf("%q does not have a solution.\n", flagParts[1])
 		help()

three/diagnostic.go

@@ -0,0 +1,144 @@
+package three
+
+import (
+	"bufio"
+	"os"
+)
+
+type report struct {
+	gammaRate    int
+	epsilonRate  int
+	oxygenRating int
+	co2Rating    int
+	values       []string
+}
+
+func (r *report) read(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		r.values = append(r.values, scanner.Text())
+	}
+
+	return nil
+}
+
+func (r *report) computePowerConsumption() {
+	if len(r.values) == 0 {
+		return
+	}
+
+	inputLength := len(r.values[0])
+
+	// Loop over every bit of the input
+	for i := 0; i < inputLength; i++ {
+		ones := 0
+		zeros := 0
+
+		// Loop over every value to determine the most and least common bit values
+		for _, value := range r.values {
+			if value[i] == '1' {
+				ones++
+			} else {
+				zeros++
+			}
+		}
+
+		if ones > zeros {
+			r.gammaRate = r.gammaRate<<1 + 1
+			r.epsilonRate = r.epsilonRate<<1 + 0
+		} else {
+			r.gammaRate = r.gammaRate<<1 + 0
+			r.epsilonRate = r.epsilonRate<<1 + 1
+		}
+	}
+}
+
+func (r *report) computeOxygenRating() {
+	if len(r.values) == 0 {
+		return
+	}
+
+	inputLength := len(r.values[0])
+
+	filtered := r.values
+	// Loop over every bit of the input
+	for i := 0; i < inputLength; i++ {
+		if len(filtered) == 1 {
+			break
+		}
+
+		ones := []string{}
+		zeros := []string{}
+
+		// Loop over every value to determine the most and least common bit values
+		for _, value := range filtered {
+			if value[i] == '1' {
+				ones = append(ones, value)
+			} else {
+				zeros = append(zeros, value)
+			}
+		}
+
+		if len(ones) >= len(zeros) {
+			filtered = ones
+		} else {
+			filtered = zeros
+		}
+	}
+
+	for _, b := range filtered[0] {
+		if b == '1' {
+			r.oxygenRating = r.oxygenRating<<1 + 1
+		} else {
+			r.oxygenRating = r.oxygenRating<<1 + 0
+		}
+	}
+}
+
+func (r *report) computeCO2Rating() {
+	if len(r.values) == 0 {
+		return
+	}
+
+	inputLength := len(r.values[0])
+
+	filtered := r.values
+	// Loop over every bit of the input
+	for i := 0; i < inputLength; i++ {
+		if len(filtered) == 1 {
+			break
+		}
+
+		ones := []string{}
+		zeros := []string{}
+
+		// Loop over every value to determine the most and least common bit values
+		for _, value := range filtered {
+			if value[i] == '1' {
+				ones = append(ones, value)
+			} else {
+				zeros = append(zeros, value)
+			}
+		}
+
+		if len(ones) < len(zeros) {
+			filtered = ones
+		} else {
+			filtered = zeros
+		}
+	}
+
+	for _, b := range filtered[0] {
+		if b == '1' {
+			r.co2Rating = r.co2Rating<<1 + 1
+		} else {
+			r.co2Rating = r.co2Rating<<1 + 0
+		}
+	}
+}

three/diagnostic_test.go

@@ -0,0 +1,43 @@
+package three
+
+import "testing"
+
+var test_input = []string{
+	"00100",
+	"11110",
+	"10110",
+	"10111",
+	"10101",
+	"01111",
+	"00111",
+	"11100",
+	"10000",
+	"11001",
+	"00010",
+	"01010",
+}
+
+func Test_read(t *testing.T) {
+	r := report{}
+	if err := r.read("input.txt"); err != nil {
+		t.FailNow()
+	}
+
+	if len(r.values) != 1000 {
+		t.Logf("Expected 1000 values, found %d", len(r.values))
+		t.Fail()
+	}
+}
+
+func Test_computeCO2Rating(t *testing.T) {
+	r := report{
+		values: test_input,
+	}
+
+	r.computeCO2Rating()
+
+	if r.co2Rating != 10 {
+		t.Logf("Expected a CO2 rating of 10, got %d", r.co2Rating)
+		t.Fail()
+	}
+}

three/main.go

@@ -0,0 +1,34 @@
+package three
+
+import "fmt"
+
+type Three struct {
+	report report
+}
+
+func Init(filepath string) *Three {
+	three := &Three{
+		report: report{},
+	}
+
+	three.report.read(filepath)
+
+	return three
+}
+
+func (d *Three) Answer() string {
+	d.report.computePowerConsumption()
+	return fmt.Sprintf("The power rates are gamma: %d, epsilon: %d, for %d total", d.report.gammaRate, d.report.epsilonRate, d.report.gammaRate*d.report.epsilonRate)
+}
+
+func (d *Three) FollowUp() string {
+	d.report.computeOxygenRating()
+	d.report.computeCO2Rating()
+
+	return fmt.Sprintf(
+		"The oxygen rating is %d and CO2 rating is %d, for a life support rating of %d",
+		d.report.oxygenRating,
+		d.report.co2Rating,
+		d.report.oxygenRating * d.report.co2Rating,
+	)
+}