diff --git a/day-4/main.go b/day-4/main.go
new file mode 100644
index 0000000..d24ba2a
--- /dev/null
+++ b/day-4/main.go
@@ -0,0 +1,271 @@
+/* Day 4: Giant Squid */
+// TODO: Redo this whole thing with bit arrays instead
+package main
+
+import (
+	"AoC2021/utils/timer"
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func check(e error) {
+	if e != nil {
+		fmt.Println("Oh snap!")
+		panic(e)
+	}
+}
+
+func main() {
+	fmt.Println("--- Day 4: Giant Squid ---")
+	timer.Start()
+	part1()
+	timer.Tick()
+	fmt.Println()
+
+	part2()
+	timer.Tick()
+	fmt.Println()
+}
+
+type Card = [][]string
+
+func readData(input *os.File) ([]string, []Card) {
+	scanner := bufio.NewScanner(input)
+
+	var draws []string
+
+	if scanner.Scan() {
+		draws = strings.Split(scanner.Text(), ",")
+	}
+
+	var cards []Card
+	cardIdx := -1 // the first new line will initialize card 0
+	rowIdx := 0
+
+	// fmt.Printf("Created cards %s", cards)
+	for scanner.Scan() {
+		line := scanner.Text()
+		switch {
+		case line == "": // when we hit an epty line, initialize a new card
+			cards = append(cards, Card{})
+			cardIdx += 1
+			rowIdx = 0
+			//fmt.Printf("Added card %d to cards {%s}\n", cardIdx, cards)
+		default:
+			rowVals := strings.Fields(line)
+			//fmt.Printf("Attempting to push [%s] to card %d row %d {%s}\n", line, cardIdx, rowIdx, cards[cardIdx])
+			cards[cardIdx] = append(cards[cardIdx], rowVals)
+			rowIdx += 1
+		}
+	}
+
+	return draws, cards
+}
+
+type MarkedCard = [][]bool
+
+func initializeMarks(cards []Card) []MarkedCard {
+	// create a number of marked cards equal to the number of bingo cards
+	cardsLen := len(cards)
+	marks := make([]MarkedCard, cardsLen)
+	// find the number of rows on a card
+	rowCount := len(cards[0])
+	colCount := len(cards[0][0])
+
+	for cIdx := 0; cIdx < cardsLen; cIdx++ {
+		marks[cIdx] = make([][]bool, rowCount)
+		for rIdx := 0; rIdx < rowCount; rIdx++ {
+			//fmt.Printf("Attempting to add row %d to card %d", rIdx, cIdx)
+			//fmt.Println(marks[cIdx])
+			marks[cIdx][rIdx] = make([]bool, colCount)
+		}
+	}
+
+	return marks
+}
+
+func markCards(cards []Card, marks []MarkedCard, draw string) []MarkedCard {
+	for cIdx, card := range cards {
+		for rowIdx, row := range card {
+			for colIdx, value := range row {
+				if value == draw {
+					marks[cIdx][rowIdx][colIdx] = true
+				}
+			}
+		}
+	}
+
+	return marks
+}
+
+// TODO: currently assumes only one card will win per round
+func findWinningCardIdx(marks []MarkedCard) int {
+	for cIdx, card := range marks {
+		if matchesRow(card) || matchesColumn(card) {
+			return cIdx
+		}
+	}
+
+	return -1
+}
+
+func matchesRow(card MarkedCard) bool {
+	for _, row := range card {
+		marks := 0
+		for _, value := range row {
+			if value {
+				marks += 1
+			}
+		}
+		if marks == len(row) {
+			return true
+		}
+	}
+	return false
+}
+
+func matchesColumn(card MarkedCard) bool {
+	rowCount := len(card)
+	colCount := len(card[0])
+	for colIdx := 0; colIdx < colCount; colIdx++ {
+		marks := 0
+		for rowIdx := 0; rowIdx < rowCount; rowIdx++ {
+			if card[rowIdx][colIdx] {
+				marks += 1
+			}
+		}
+
+		if marks == colCount {
+			return true
+		}
+	}
+	return false
+}
+
+func getCardScore(card Card, mark MarkedCard) int {
+	score := 0
+
+	// sum up all the non-marked bingo spots
+	for rIdx, row := range card {
+		for cIdx, strVal := range row {
+			if !mark[rIdx][cIdx] {
+				value, err := strconv.Atoi(strVal)
+				check(err)
+
+				score += value
+			}
+		}
+	}
+	return score
+}
+
+func part1() {
+	fmt.Println("* Part 1 *")
+	fmt.Println(" Goal: Figure out which bingo board will win first.")
+	fmt.Println(" Answer: What will your final score be if you choose that board?")
+
+	input, err := os.Open("./input.txt")
+	check(err)
+	defer input.Close()
+
+	draws, cards := readData(input)
+	marks := initializeMarks(cards)
+
+	//fmt.Printf("Read in %d draws and %d cards\n", len(draws), len(cards))
+	//fmt.Printf("Initialized %d mark cards\n", len(marks))
+	//fmt.Printf("First card %s\n", cards[0])
+	//fmt.Println(marks[0])
+
+	drawTimes := 0
+	winningCardIdx := -1
+	lastDraw := 0
+	score := 0
+	for _, draw := range draws {
+		drawTimes += 1
+		marks = markCards(cards, marks, draw)
+		winningCardIdx = findWinningCardIdx(marks)
+		if winningCardIdx >= 0 {
+			winningCard := cards[winningCardIdx]
+			winningMarks := marks[winningCardIdx]
+			score = getCardScore(winningCard, winningMarks)
+
+			// multiply by the last drawn tile
+			mult, err := strconv.Atoi(draw)
+			check(err)
+
+			lastDraw = mult
+			score *= mult
+
+			break
+		}
+	}
+
+	fmt.Printf("After %d draws, card #%d won on a %d with a score of %d\n", drawTimes, winningCardIdx, lastDraw, score)
+}
+
+func part2() {
+	fmt.Println("* Part 2 *")
+	fmt.Println(" Goal: Figure out which board will win last.")
+	fmt.Println(" Answer: Once it wins, what would its final score be?")
+
+	input, err := os.Open("./input.txt")
+	check(err)
+	defer input.Close()
+
+	draws, cards := readData(input)
+	marks := initializeMarks(cards)
+
+	drawTimes := 0
+	lastDraw := 0
+	score := 0
+	foundLoser := false
+
+	for _, draw := range draws {
+		if foundLoser {
+			break
+		}
+
+		drawTimes += 1
+		marks = markCards(cards, marks, draw)
+		winningCardIdx := findWinningCardIdx(marks)
+
+		eliminatedCards := 0
+		for winningCardIdx > -1 {
+			// if there's only one card left, it's the losingist one
+			if len(marks) == 1 {
+				score = getCardScore(cards[0], marks[0])
+
+				// multiply by the last drawn tile
+				mult, err := strconv.Atoi(draw)
+				check(err)
+
+				lastDraw = mult
+				score *= mult
+				foundLoser = true
+				break
+			}
+
+			eliminatedCards += 1
+			// if a card wins, just remove it from the list of cards and don't track it anymore
+			cards[winningCardIdx] = cards[len(cards)-1]
+			cards[len(cards)-1] = Card{}
+			cards = cards[:len(cards)-1]
+
+			marks[winningCardIdx] = marks[len(marks)-1]
+			marks[len(marks)-1] = MarkedCard{}
+			marks = marks[:len(marks)-1]
+
+			winningCardIdx = findWinningCardIdx(marks)
+		}
+		if eliminatedCards > 0 {
+			//fmt.Printf("Round %d: Eliminated %d cards with a %s (%d remaining)\n", drawTimes, eliminatedCards, draw, len(cards))
+		}
+	}
+
+	//fmt.Println("Card: ", cards[0])
+	//fmt.Println("Mark: ", marks[0])
+	fmt.Printf("After %d draws, the losingist card won on a %d with a score of %d\n", drawTimes, lastDraw, score)
+}
diff --git a/day-4/main_test.go b/day-4/main_test.go
new file mode 100644
index 0000000..a30f81c
--- /dev/null
+++ b/day-4/main_test.go
@@ -0,0 +1,11 @@
+package main
+
+import (
+	assert "AoC2021/utils/testing"
+	"testing"
+)
+
+func TestDay4(t *testing.T) {
+	assert.IsTrue(t, true, "cool")
+	assert.StrEquals(t, "foo", "bar", "baz")
+}