Re-implement a solution for the first day 1 puzzle, move common code into a library package.

2018/internal/calibration/calibration.go

@@ -0,0 +1,38 @@
+package calibration
+
+import (
+	"bufio"
+	"os"
+	"strconv"
+)
+
+type Set map[int]struct{}
+
+// ScanFrequencies iterates over a list of frequencies (provided as an open
+// file handle), compares against a list of frequencies already seen and a 'current' frequency counter,
+// and returns `true` when a duplicate frequency is found. Integer value returned is the new, adjusted frequency
+func ScanFrequencies(freqFile string, seen *Set, frequency int) (int, bool) {
+	file, err := os.Open(os.Args[1])
+	if err != nil {
+		panic(err)
+	}
+
+	duplicateFound := false
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		y, err := strconv.Atoi(scanner.Text())
+		if err != nil {
+			panic(err)
+		}
+		frequency += y
+		if _, ok := (*seen)[frequency]; ok {
+			duplicateFound = true
+			break
+		}
+
+		(*seen)[frequency] = struct{}{}
+	}
+
+	file.Close()
+	return frequency, duplicateFound
+}