day 9 and 10

day-10/main.go

@@ -0,0 +1,215 @@
+/* Day 10: Syntax Scoring */
+package main
+
+import (
+	"AoC2021/utils/arrays"
+	"AoC2021/utils/log"
+	"AoC2021/utils/timer"
+	"bufio"
+	"os"
+	"sort"
+	"strings"
+)
+
+func check(e error) {
+	if e != nil {
+		log.Println(log.DEBUG, "Oh snap!")
+		panic(e)
+	}
+}
+
+func main() {
+	log.Println(log.NORMAL, "--- Day 10: Syntax Scoring ---")
+	timer.Start()
+	part1()
+	timer.Tick()
+	log.Println(log.NORMAL)
+
+	part2()
+	timer.Tick()
+	log.Println(log.NORMAL)
+}
+
+func part1() {
+	log.LOG_LEVEL = log.DEBUG
+	log.Println(log.NORMAL, "* Part 1 *")
+	log.Println(log.NORMAL, " Goal: Find the first illegal character in each corrupted line of the navigation subsystem.")
+	log.Println(log.NORMAL, " Answer: What is the total syntax error score for those errors?")
+
+	input, err := os.Open("./input.txt")
+	check(err)
+	defer input.Close()
+
+	scanner := bufio.NewScanner(input)
+	lines := 0
+	tokenCount := 0
+	totalScore := 0
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		_, errScore := validateNavLine(line)
+		totalScore += errScore
+		lines++
+		tokenCount += len(line)
+	}
+
+	log.Printf(log.NORMAL, "Read %d lines with %d tokens from input\n", lines, tokenCount)
+	log.Printf(log.NORMAL, "The total syntax error score is %d\n", totalScore)
+}
+
+func part2() {
+	log.Println(log.NORMAL, "* Part 2 *")
+	log.Println(log.NORMAL, " Goal: Find the completion string for each incomplete line, score the completion strings, and sort the scores.")
+	log.Println(log.NORMAL, " Answer: What is the middle score?")
+
+	input, err := os.Open("./input.txt")
+	check(err)
+	defer input.Close()
+
+	scanner := bufio.NewScanner(input)
+	lines := 0
+	tokenCount := 0
+
+	var autoScores []int
+
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		lines++
+		tokenCount += len(line)
+
+		remainingStr, errScore := validateNavLine(line)
+		if errScore > 0 || len(remainingStr) == 0 {
+			continue
+		}
+
+		autoScores = append(autoScores, getAutoScore(remainingStr))
+	}
+
+	// stort the scores
+	sort.Slice(autoScores, func(i, j int) bool { return autoScores[i] < autoScores[j] })
+	// find the middle-ist index
+	middleIdx := len(autoScores) / 2
+
+	log.Printf(log.NORMAL, "Read %d lines with %d tokens from input\n", lines, tokenCount)
+	log.Printf(log.NORMAL, "Autocompleted %d lines\n", len(autoScores))
+	log.Printf(log.NORMAL, "The middle-ist auto-correct score at pos %d is %d\n", middleIdx, autoScores[middleIdx])
+}
+
+// validates the nav line and returns a non-zero value as a syntax error score
+func BAD_validateNavLine(line string) int {
+	// split the line into tokens
+	tokens := strings.Split(line, "")
+	invalidStr := "An invalid token '%s' was found at position %3d while validating string: %s\n"
+
+	// I thought of doing this generically but there are only 4 hard-coded options so just do it manually
+	parens, brackets, braces, gators := 0, 0, 0, 0
+
+	for idx, token := range tokens {
+		switch token {
+		case "(":
+			parens++
+		case "[":
+			brackets++
+		case "{":
+			braces++
+		case "<":
+			gators++
+		case ")":
+			if parens > 0 {
+				parens--
+			} else {
+				log.Printf(log.DEBUG, invalidStr, token, idx, line)
+				return 3
+			}
+		case "]":
+			if brackets > 0 {
+				brackets--
+			} else {
+				log.Printf(log.DEBUG, invalidStr, token, idx, line[:idx+1])
+				return 57
+			}
+		case "}":
+			if braces > 0 {
+				braces--
+			} else {
+				log.Printf(log.DEBUG, invalidStr, token, idx, line)
+				return 1197
+			}
+		case ">":
+			if gators > 0 {
+				gators--
+			} else {
+				log.Printf(log.DEBUG, invalidStr, token, idx, line)
+				return 25137
+			}
+		}
+	}
+
+	return 0
+}
+
+func validateNavLine(line string) (string, int) {
+	reducedLine := reduceNavLine(line)
+	if len(reducedLine) == 0 {
+		return reducedLine, 0
+	}
+	// find the first closing token
+	firstCloseTokenIdx := strings.IndexAny(reducedLine, ")]}>")
+	// if no closing tokens are found, this is just an incomplete line (not corrupt)
+	if firstCloseTokenIdx == -1 {
+		return reducedLine, 0
+	}
+	log.Printf(log.DIAGNOSTIC, "First invalid token is at %d on %s\n", firstCloseTokenIdx, reducedLine)
+	switch reducedLine[firstCloseTokenIdx] {
+	case ')':
+		return reducedLine, 3
+	case ']':
+		return reducedLine, 57
+	case '}':
+		return reducedLine, 1197
+	case '>':
+		return reducedLine, 25137
+	}
+
+	return reducedLine, 0
+}
+
+func reduceNavLine(line string) string {
+	//recursively remove empty chunks from the line
+	oldLen := len(line)
+	for {
+		line = strings.ReplaceAll(line, "()", "")
+		line = strings.ReplaceAll(line, "[]", "")
+		line = strings.ReplaceAll(line, "{}", "")
+		line = strings.ReplaceAll(line, "<>", "")
+
+		if len(line) == oldLen {
+			break
+		}
+		oldLen = len(line)
+	}
+
+	return line
+}
+
+// get an auto-complete score from a line that has already been reduced
+func getAutoScore(reducedLine string) int {
+	// we'll have to auto-complete tokens in REVERSE order of the opening tokens in the reducedLine
+	score := 0
+	for _, token := range arrays.Reverse(strings.Split(reducedLine, "")) {
+		score *= 5
+		switch token {
+		case "(":
+			score += 1
+		case "[":
+			score += 2
+		case "{":
+			score += 3
+		case "<":
+			score += 4
+		}
+	}
+
+	return score
+}