2019 Day 16 Complete

2019/day16/input

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+59708072843556858145230522180223745694544745622336045476506437914986923372260274801316091345126141549522285839402701823884690004497674132615520871839943084040979940198142892825326110513041581064388583488930891380942485307732666485384523705852790683809812073738758055115293090635233887206040961042759996972844810891420692117353333665907710709020698487019805669782598004799421226356372885464480818196786256472944761036204897548977647880837284232444863230958576095091824226426501119748518640709592225529707891969295441026284304137606735506294604060549102824977720776272463738349154440565501914642111802044575388635071779775767726626682303495430936326809

2019/day16/main.go

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+package main
+
+import (
+	"fmt"
+	"math"
+	"strings"
+
+	helpers "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := helpers.StdinToString()
+	part1(inp)
+	fmt.Println()
+	part2(inp)
+}
+
+func part1(inp string) {
+	var intinp []int
+	for _, v := range inp {
+		intinp = append(intinp, int(byte(v)-'0'))
+	}
+	for i := 0; i < 100; i++ {
+		intinp = runFFT(intinp)
+	}
+	fmt.Println("# Part 1:")
+	fmt.Println(intinp[:8])
+}
+
+// Well, brute force isn't going to work
+// Fortunately, the next instance of each digit is actually just the
+// sum of all digits after it (%10)
+func part2(inp string) {
+	fullInput := strings.Repeat(inp, 10000)
+	messageOffset := helpers.Atoi(inp[:7])
+	var intinp []int
+	for _, v := range fullInput[messageOffset:] {
+		intinp = append(intinp, int(byte(v)-'0'))
+	}
+	for iter := 0; iter < 100; iter++ {
+		sum := 0
+		for i := len(intinp) - 1; i >= 0; i-- {
+			sum += intinp[i]
+			intinp[i] = sum % 10
+		}
+	}
+
+	fmt.Println("# Part 2:")
+	for _, c := range intinp[:8] {
+		fmt.Print(helpers.Itoa(c))
+	}
+	fmt.Println()
+}
+
+func runFFT(inp []int) []int {
+	var result []int
+	for k := range inp {
+		pattern := getPattern(len(inp), k+1)
+		var wrk int
+		for k, iv := range inp {
+			wrk = wrk + (iv * pattern[k])
+		}
+		result = append(result, helpers.AbsInt(wrk%10))
+	}
+	return result
+}
+
+func getPattern(length, iter int) []int {
+	var ret []int
+	pattern := []int{0, 1, 0, -1}
+	var idx int
+	for len(ret) < length+1 {
+		wrkIter := iter
+		for ; wrkIter > 0; wrkIter-- {
+			ret = append(ret, pattern[idx])
+		}
+		idx = (idx + 1) % len(pattern)
+	}
+	return ret[1 : length+1]
+}
+
+func intSliceToInt(inp []int) int {
+	var ret int
+	for k := len(inp) - 1; k >= 0; k-- {
+		ret = ret + (inp[k] * int(math.Pow10(len(inp)-k-1)))
+	}
+	return ret
+}

2019/day16/testinput1

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+12345678