2020-day15 so close :( 600/209. difficult to just understand the prompt. brute forced a dictionary for pt 2

2017-day10 weird fake hashing, xor and hexadecimals

2020/day15/main.go

@@ -15,32 +15,47 @@ func main() {
 	flag.Parse()
 	fmt.Println("Running part", part)
 
+	var ans int
 	if part == 1 {
-		ans := part1(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
-		fmt.Println("Output:", ans)
+		ans = rambunctiousRecitation(util.ReadFile("./input.txt"), 2020)
 	} else {
-		ans := part2(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
-		fmt.Println("Output:", ans)
+		// brute force, takes ~5seconds to run
+		ans = rambunctiousRecitation(util.ReadFile("./input.txt"), 30000000)
 	}
+	fmt.Println("Output:", ans)
 }
 
-func part1(input string) int {
-	parsed := parseInput(input)
-	_ = parsed
-
-	return 0
-}
-
-func part2(input string) int {
-	return 0
-}
-
-func parseInput(input string) (ans []int) {
-	lines := strings.Split(input, "\n")
-	for _, l := range lines {
-		ans = append(ans, mathutil.StrToInt(l))
+func rambunctiousRecitation(input string, turnToReturn int) int {
+	var startingNums []int
+	for _, num := range strings.Split(input, ",") {
+		startingNums = append(startingNums, mathutil.StrToInt(num))
 	}
-	return ans
+
+	said := map[int][]int{}
+	var numSaidLast int
+	// populate the starting map with the numbers from the input
+	for i, num := range startingNums {
+		said[num] = append(said[num], i+1)
+		numSaidLast = num
+	}
+
+	// then picking up from the next turn (len of input), continue until the
+	// desired turn is reached
+	for i := len(startingNums); i <= turnToReturn; i++ {
+		indexSlice := said[numSaidLast]
+		// if the length of the slice of incides is 1, that means it was only
+		// called once. Say zero, add to the zero slice of indices
+		if len(indexSlice) == 1 {
+			numSaidLast = 0
+			said[0] = append(said[0], i)
+		} else {
+			// otherwise determine the diff between the last 2 times it was said
+			length := len(indexSlice)
+			numSaidLast = indexSlice[length-1] - indexSlice[length-2]
+			// add this index i to the indices slice for the number that is said
+			said[numSaidLast] = append(said[numSaidLast], i)
+		}
+	}
+
+	return numSaidLast
 }