2021 Day 4

2021/day4/main.go

@@ -0,0 +1,148 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/fatih/color"
+	"github.com/jdkaplan/advent-of-code/aoc"
+)
+
+type input struct {
+	numbers []int
+	boards  []board
+}
+
+func parseInput(text string) input {
+	sections := strings.Split(text, "\n\n")
+	var nums []int
+	for _, n := range strings.Split(sections[0], ",") {
+		nums = append(nums, aoc.MustInt(n))
+	}
+	var boards []board
+	for _, block := range sections[1:] {
+		b := newBoard()
+		for r, row := range strings.Split(block, "\n") {
+			for c, n := range strings.Fields(row) {
+				b.nums[r][c] = aoc.MustInt(n)
+			}
+		}
+		boards = append(boards, b)
+	}
+	return input{numbers: nums, boards: boards}
+}
+
+type board struct {
+	nums   *[5][5]int
+	marked *[5][5]bool
+	won    bool
+}
+
+func newBoard() board {
+	return board{
+		nums:   &[5][5]int{},
+		marked: &[5][5]bool{},
+	}
+}
+
+func (b board) String() string {
+	var s strings.Builder
+	for r, row := range b.nums {
+		for c, n := range row {
+			if b.marked[r][c] {
+				color.New(color.FgGreen, color.Bold).Fprintf(&s, "%2d ", n)
+			} else {
+				fmt.Fprintf(&s, "%2d ", n)
+			}
+		}
+		s.WriteRune('\n')
+	}
+	return s.String()
+}
+
+func (b *board) call(x int) (win bool) {
+	if b.won {
+		return false
+	}
+	for r, row := range b.nums {
+		for c, n := range row {
+			if n == x {
+				b.marked[r][c] = true
+				if b.win(r, c) {
+					return true
+				}
+			}
+		}
+	}
+	return
+}
+
+func (b board) win(r, c int) bool {
+	return b.winRow(r) || b.winCol(c)
+}
+
+func (b board) winRow(r int) bool {
+	for c := 0; c < 5; c++ {
+		if !b.marked[r][c] {
+			return false
+		}
+	}
+	return true
+}
+
+func (b board) winCol(c int) bool {
+	for r := 0; r < 5; r++ {
+		if !b.marked[r][c] {
+			return false
+		}
+	}
+	return true
+}
+
+func (b board) score(x int) int {
+	var sum int
+	for r, row := range b.nums {
+		for c, n := range row {
+			if !b.marked[r][c] {
+				sum += n
+			}
+		}
+	}
+	return x * sum
+}
+
+func part1(text string) int {
+	inp := parseInput(text)
+	for _, n := range inp.numbers {
+		for _, b := range inp.boards {
+			if b.call(n) {
+				return b.score(n)
+			}
+		}
+	}
+	return len(inp.numbers)
+}
+
+func part2(text string) int {
+	inp := parseInput(text)
+	var wins int
+	for _, n := range inp.numbers {
+		for i, b := range inp.boards {
+			if b.call(n) {
+				// Set on the original in inp, not the copy in b.
+				inp.boards[i].won = true
+				wins++
+				if wins == len(inp.boards) {
+					return b.score(n)
+				}
+			}
+		}
+	}
+	return len(inp.numbers)
+}
+
+func main() {
+	text := aoc.ReadFile("./input/day4.txt")
+	fmt.Println(part1(text))
+	fmt.Println(part2(text))
+}