AdventOfCode2021/04/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

func makeScanner(test bool) *bufio.Scanner {
	var f *os.File
	if test {
		f, _ = os.Open("inputs/testinput")
	} else {
		f, _ = os.Open("inputs/input")
	}
	reader := bufio.NewReader(f)
	return bufio.NewScanner(reader)
}

func mustAtoi(line string) int {
	i, err := strconv.Atoi(line)
	if err != nil {
		panic(err)
	}
	return i
}

func convertDraws(d []string) []int {
	r := make([]int, len(d))
	for i := range d {
		r[i] = mustAtoi(d[i])
	}
	return r
}

func contains(i int, a []int) bool {
	for _, j := range a {
		if i == j {
			return true
		}
	}
	return false
}

func bingo(set map[int]struct{}, drawnNumbers []int) bool {
	hits := 0
	for _, i := range drawnNumbers {
		if _, ok := set[i]; ok {
			hits++
		}
	}
	if hits == 5 {
		return true
	}
	return false
}

// a bingo card like this:
// 60 79 46  9 58
// 97 81  6 94 84
// 38 40 17 61 29
// 11 28  0 91 15
// 24 77 34 59 36
// turns into this:
// rows: [][60 79 46  9 58][97 81  6 94 84]...
// columns: [][60 97 38 11 24][79 81 40 28 77]...
// so that checking all possible hits is easier
// we use maps and not arrays to also make the lookups quicker

type bingoCard struct {
	allNumbers []int
	rows       []map[int]struct{}
	columns    []map[int]struct{}
	winner     bool
}

func readBingoCard(scanner *bufio.Scanner) bingoCard {
	card := bingoCard{
		allNumbers: []int{},
		rows:       []map[int]struct{}{0: {}, 1: {}, 2: {}, 3: {}, 4: {}},
		columns:    []map[int]struct{}{0: {}, 1: {}, 2: {}, 3: {}, 4: {}},
	}

	for i := 0; i < 5; i++ {
		scanner.Scan()
		row := strings.Split(scanner.Text(), " ")
		var col int
		for _, p := range row {
			if p != "" {
				num := mustAtoi(p)
				card.allNumbers = append(card.allNumbers, num)
				card.rows[i][num] = struct{}{}
				card.columns[col][num] = struct{}{}
				col++
			}
		}
	}
	return card
}

func checkBoard(currentNumbers []int, card bingoCard) bool {
	for _, row := range card.rows {
		if bingo(row, currentNumbers) {
			return true
		}
	}
	for _, col := range card.columns {
		if bingo(col, currentNumbers) {
			return true
		}
	}
	return false
}

func scoreBoard(currentNumbers []int, card bingoCard) int {
	totalUncalled := 0
	for _, i := range card.allNumbers {
		if !contains(i, currentNumbers) {
			totalUncalled += i
		}
	}
	return totalUncalled * currentNumbers[len(currentNumbers)-1]
}

func partOne() {
	scanner := makeScanner(false)

	scanner.Scan()
	draws := convertDraws(strings.Split(scanner.Text(), ","))
	cards := []bingoCard{}

	for scanner.Scan() {
		cards = append(cards, readBingoCard(scanner))
	}
	for i := range draws {
		for _, card := range cards {
			winner := checkBoard(draws[0:i], card)
			if winner {
				fmt.Println(scoreBoard(draws[0:i], card))
				return
			}
		}
	}
}

func partTwo() {
	scanner := makeScanner(false)

	scanner.Scan()
	draws := convertDraws(strings.Split(scanner.Text(), ","))
	cards := []bingoCard{}

	for scanner.Scan() {
		cards = append(cards, readBingoCard(scanner))
	}

	winnerCount := 0
	for i := range draws {
		for j, card := range cards {
			if !card.winner {
				winner := checkBoard(draws[0:i], card)
				if winner {
					cards[j].winner = true
					winnerCount++
					if winnerCount == len(cards) {
						// that was the last one!
						fmt.Println(scoreBoard(draws[0:i], card))
					}
				}
			}
		}
	}
}