Advent of Code 2023 - Day 3

aoc2023_d3.go

package d3

import (
	"bufio"
	"io"
	"regexp"
	"strconv"
)

func Must(err error) {
	if err != nil {
		panic(err)
	}
}

func getSum(numbers []int) int {
	total := 0
	for _, num := range numbers {
		total += num
	}
	return total
}

// idea:
// find all numbers and their index ranges
// look for symbol around their index ranges
func d3_1(r io.Reader) int {
	numberLinesStartTopIdx := map[int][][3]int{}
	symbolLinesStartTopIdx := map[int]map[int]bool{}
	reNums := regexp.MustCompile(`\d+`)

	fileScanner := bufio.NewScanner(r)
	fileScanner.Split(bufio.ScanLines)
	lineNo := 0
	for fileScanner.Scan() {
		numberLinesStartTopIdx[lineNo] = [][3]int{}
		lineBytes := fileScanner.Bytes()
		for i, c := range lineBytes {
			if (c >= '0' && c <= '9') || c == '.' {
				continue
			} else {
				if val, ok := symbolLinesStartTopIdx[lineNo]; !ok {
					symbolLinesStartTopIdx[lineNo] = map[int]bool{i: true}
				} else {
					val[i] = true
				}
			}
		}

		nums := reNums.FindAllIndex(lineBytes, -1)
		for _, numGroup := range nums {
			num, err := strconv.Atoi(string(lineBytes[numGroup[0]:numGroup[1]]))
			Must(err)
			numberLinesStartTopIdx[lineNo] = append(numberLinesStartTopIdx[lineNo], [3]int{numGroup[0], numGroup[1], num})
		}
		lineNo++
	}

	validNumbers := []int{}

	for lineNo, numGroups := range numberLinesStartTopIdx {
		for _, numGroup := range numGroups {
			// start or end of number
			if symbolLine, ok := symbolLinesStartTopIdx[lineNo]; !ok {
				// nothing on the same line
			} else if symbolLine[numGroup[0]-1] || symbolLine[numGroup[1]] {
				validNumbers = append(validNumbers, numGroup[2])
				continue
			}
			// line on top or under
			for i := numGroup[0] - 1; i <= numGroup[1]; i++ {
				if symbolLine, ok := symbolLinesStartTopIdx[lineNo-1]; !ok {
					// nothing on the same line
				} else if symbolLine[i] {
					validNumbers = append(validNumbers, numGroup[2])
					break
				}
				if symbolLine, ok := symbolLinesStartTopIdx[lineNo+1]; !ok {
					// nothing on the same line
				} else if symbolLine[i] {
					validNumbers = append(validNumbers, numGroup[2])
					break
				}
			}
		}
	}
	return getSum(validNumbers)
}

func d3_2(r io.Reader) int {
	numberLinesStartTopIdx := map[int][][3]int{}
	symbolLinesStartTopIdx := map[int]map[int]bool{}
	reNums := regexp.MustCompile(`\d+`)

	fileScanner := bufio.NewScanner(r)
	fileScanner.Split(bufio.ScanLines)
	lineNo := 0
	for fileScanner.Scan() {
		numberLinesStartTopIdx[lineNo] = [][3]int{}
		lineBytes := fileScanner.Bytes()
		for i, c := range lineBytes {
			if c == '*' {
				if val, ok := symbolLinesStartTopIdx[lineNo]; !ok {
					symbolLinesStartTopIdx[lineNo] = map[int]bool{i: true}
				} else {
					val[i] = true
				}
			}
		}
		nums := reNums.FindAllIndex(lineBytes, -1)
		for _, numGroup := range nums {
			num, err := strconv.Atoi(string(lineBytes[numGroup[0]:numGroup[1]]))
			Must(err)
			numberLinesStartTopIdx[lineNo] = append(numberLinesStartTopIdx[lineNo], [3]int{numGroup[0], numGroup[1], num})
		}
		lineNo++
	}

	totalSum := 0
	for lineNo, startStops := range symbolLinesStartTopIdx {
		for gearIdx := range startStops {
			neighborNumsCount := 0
			neighborNums := []int{}

			for _, numGroup := range numberLinesStartTopIdx[lineNo-1] {
				if gearIdx >= numGroup[0]-1 && gearIdx <= numGroup[1] {
					neighborNumsCount++
					neighborNums = append(neighborNums, numGroup[2])
				}
			}

			for _, numGroup := range numberLinesStartTopIdx[lineNo] {
				if gearIdx >= numGroup[0]-1 && gearIdx <= numGroup[1] {
					neighborNumsCount++
					neighborNums = append(neighborNums, numGroup[2])
				}
			}

			for _, numGroup := range numberLinesStartTopIdx[lineNo+1] {
				if gearIdx >= numGroup[0]-1 && gearIdx <= numGroup[1] {
					neighborNumsCount++
					neighborNums = append(neighborNums, numGroup[2])
				}
			}
			if neighborNumsCount == 2 {
				totalSum += neighborNums[0] * neighborNums[1]
			}
		}
	}

	return totalSum
}