d3p3

d3/d3.go

@@ -36,3 +36,45 @@ func D3(input string) int64 {
 
 	return gammaNum * epsilonNum
 }
+
+func rating(binaries []string, position int, path func([]string, []string) []string) string {
+	if len(binaries) == 1 {
+		return binaries[0]
+	}
+
+	ones := make([]string, 0, len(binaries)/2) // allocate at least half original slice
+	zeroes := make([]string, 0, len(binaries)/2)
+	for _, binary := range binaries {
+		if binary[position] == '1' {
+			ones = append(ones, binary)
+		} else {
+			zeroes = append(zeroes, binary)
+
+		}
+	}
+
+	return rating(path(ones, zeroes), position+1, path)
+}
+
+func D3P2(input string) int64 {
+	binaries := strings.Split(strings.TrimSpace(input), "\n")
+
+	o2predicate := func(ones, zeroes []string) []string {
+		if len(ones) == len(zeroes) || len(ones) > len(zeroes) {
+			return ones
+		}
+		return zeroes
+	}
+
+	co2predicate := func(ones, zeroes []string) []string {
+		if len(ones) == len(zeroes) || len(ones) > len(zeroes) {
+			return zeroes
+		}
+		return ones
+	}
+
+	o2rating, _ := strconv.ParseInt(rating(binaries, 0, o2predicate), 2, 64)
+	co2rating, _ := strconv.ParseInt(rating(binaries, 0, co2predicate), 2, 64)
+
+	return o2rating * co2rating
+}

d3/d3_test.go

@@ -23,3 +23,21 @@ func TestD3(t *testing.T) {
 
 	assert.EqualValues(t, 198, D3(input))
 }
+
+func TestD3P2(t *testing.T) {
+	input := `
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010`
+
+	assert.EqualValues(t, 230, D3P2(input))
+}

main.go

@@ -27,5 +27,6 @@ func main() {
 	fmt.Printf("day 2: %v\n", d2.D2(client.Day(2)))
 	fmt.Printf("day 2 part 2: %v\n", d2.D2P2(client.Day(2)))
 	fmt.Printf("day 3: %v\n", d3.D3(client.Day(3)))
+	fmt.Printf("day 3 part 2: %v\n", d3.D3P2(client.Day(3)))
 
 }