Add day 2 solution.

2018/day02-1.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"fmt"
+
+	"internal/util"
+)
+
+func main() {
+	lines := util.ReadInput()
+
+	twos := 0
+	threes := 0
+	for _, id := range lines {
+		// here we build up a map of letters and counts
+		letters := make(map[byte]int)
+		for i := 0; i < len(id); i++ {
+			letters[id[i]] += 1
+		}
+
+		// these are the values to add to the 'twos' and 'threes'
+		// count, respectively. They will only ever be 0 or 1.
+		add2 := 0
+		add3 := 0
+
+		// now we iterate over the map of letter->count, and set
+		// add2 and add3 if we find any values equal to 2 or 3
+		for _, v := range letters {
+			if v == 2 {
+				add2 = 1
+			}
+			if v == 3 {
+				add3 = 1
+			}
+		}
+
+		twos += add2
+		threes += add3
+	}
+
+	fmt.Println(twos * threes)
+}