day 3 part 1

03/main.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"math/bits"
+	"os"
+	"strconv"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+func makeScanner(test bool) *bufio.Scanner {
+	var f *os.File
+	if test {
+		f, _ = os.Open("inputs/testinput")
+	} else {
+		f, _ = os.Open("inputs/input")
+	}
+	reader := bufio.NewReader(f)
+	return bufio.NewScanner(reader)
+}
+
+func partOne() {
+	scanner := makeScanner(false)
+
+	r := map[int]int64{} // index => count of 1s
+	var lines int64
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		lines++
+		n, _ := strconv.ParseInt(line, 2, 64)
+		for i := 0; i < bits.Len(uint(n)); i++ {
+			// check if the number in the i'th column is 1, then bit-shift back to the 1s place to add it if it is
+			r[i] += (n & (1 << i)) >> i
+		}
+	}
+	var epsilon, gamma int64
+	for i, b := range r {
+		// if more than half the bits were ones, gamma gets the 1, otherwise epsilon gets the 1
+		// alternatively, this could have been an XOR operation, I suppose, once one or the other had been computed
+		if b > lines/2 {
+			gamma += 1 << i
+		} else {
+			epsilon += 1 << i
+		}
+	}
+	fmt.Println(epsilon * gamma)
+}
+
+func partTwo() {
+	scanner := makeScanner(false)
+
+	for scanner.Scan() {
+		// line := scanner.Text()
+	}
+}