✨Added Day 4 Solution

Day 4/README.md

@@ -0,0 +1,77 @@
+# Day 4: Giant Squid
+
+You're already almost 1.5km (almost a mile) below the surface of the ocean, already so deep that you can't see any sunlight. What you **can** see, however, is a giant squid that has attached itself to the outside of your submarine.
+
+Maybe it wants to play [bingo](https://en.wikipedia.org/wiki/Bingo_(American_version))?
+
+Bingo is played on a set of boards each consisting of a 5x5 grid of numbers. Numbers are chosen at random, and the chosen number is **marked** on all boards on which it appears. (Numbers may not appear on all boards.) If all numbers in any row or any column of a board are marked, that board **wins**. (Diagonals don't count.)
+
+The submarine has a **bingo subsystem** to help passengers (currently, you and the giant squid) pass the time. It automatically generates a random order in which to draw numbers and a random set of boards (your puzzle input). For example:
+
+```
+7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
+19  8  7 25 23
+20 11 10 24  4
+14 21 16 12  6
+
+14 21 17 24  4
+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7
+```
+
+After the first five numbers are drawn (`7`, `4`, `9`, `5`, and `11`), there are no winners, but the boards are marked as follows (shown here adjacent to each other to save space):
+
+```
+22 13 17 11  0         3 15  0  2 22        14 21 17 24  4
+ 8  2 23  4 24         9 18 13 17  5        10 16 15  9 19
+21  9 14 16  7        19  8  7 25 23        18  8 23 26 20
+ 6 10  3 18  5        20 11 10 24  4        22 11 13  6  5
+ 1 12 20 15 19        14 21 16 12  6         2  0 12  3  7
+```
+
+After the next six numbers are drawn (`17`, `23`, `2`, `0`, `14`, and `21`), there are still no winners:
+
+```
+22 13 17 11  0         3 15  0  2 22        14 21 17 24  4
+ 8  2 23  4 24         9 18 13 17  5        10 16 15  9 19
+21  9 14 16  7        19  8  7 25 23        18  8 23 26 20
+ 6 10  3 18  5        20 11 10 24  4        22 11 13  6  5
+ 1 12 20 15 19        14 21 16 12  6         2  0 12  3  7
+```
+
+Finally, `24` is drawn:
+
+```
+22 13 17 11  0         3 15  0  2 22        14 21 17 24  4
+ 8  2 23  4 24         9 18 13 17  5        10 16 15  9 19
+21  9 14 16  7        19  8  7 25 23        18  8 23 26 20
+ 6 10  3 18  5        20 11 10 24  4        22 11 13  6  5
+ 1 12 20 15 19        14 21 16 12  6         2  0 12  3  7
+```
+
+At this point, the third board **wins** because it has at least one complete row or column of marked numbers (in this case, the entire top row is marked: `14 21 17 24 4`).
+
+The **score** of the winning board can now be calculated. Start by finding the **sum of all unmarked numbers** on that board; in this case, the sum is `188`. Then, multiply that sum by **the number that was just called** when the board won, `24`, to get the final score, `188 * 24 = 4512`.
+
+To guarantee victory against the giant squid, figure out which board will win first. **What will your final score be if you choose that board?**
+
+# Part Two
+
+On the other hand, it might be wise to try a different strategy: let the giant squid win.
+
+You aren't sure how many bingo boards a giant squid could play at once, so rather than waste time counting its arms, the safe thing to do is to **figure out which board will win last** and choose that one. That way, no matter which boards it picks, it will win for sure.
+
+In the above example, the second board is the last to win, which happens after `13` is eventually called and its middle column is completely marked. If you were to keep playing until this point, the second board would have a sum of unmarked numbers equal to `148` for a final score of `148 * 13 = 1924`.
+
+Figure out which board will win last. **Once it wins, what would its final score be?**

Day 4/input

@@ -0,0 +1,601 @@
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+
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Day 4/main.go

@@ -0,0 +1,201 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"math"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type BingoBoardSpace struct {
+	marked bool
+	value int
+}
+
+func calculateScore(board []BingoBoardSpace, callout int, invert bool) int {
+	score := 0
+	for _, space := range board {
+		if !invert && !space.marked { score += space.value }
+		if invert && space.marked { score += space.value }
+	}
+	
+	return score * callout
+}
+
+func checkForWinner(board []BingoBoardSpace) bool {
+	for y := 0; y < 5; y++ {
+		// Horizontal
+		if board[5 * y].marked && board[5 * y + 1].marked && board[5 * y + 2].marked && board[5 * y + 3].marked && board[5 * y + 4].marked {
+			return true
+		}
+
+		// Vertical
+		if board[y].marked && board[5 + y].marked && board[10 + y].marked && board[15 + y].marked && board[20 + y].marked {
+			return true
+		}
+	}
+
+	return false
+}
+
+func partOne(callouts []int, boards [][]BingoBoardSpace) {
+	winningBoard := []BingoBoardSpace{}
+	winningCallout := 0
+
+	for _, callout := range callouts {
+		winnerFound := false
+
+		for boardIndex := range boards {
+			for spaceIndex := range boards[boardIndex] {
+				if boards[boardIndex][spaceIndex].value == callout {
+					boards[boardIndex][spaceIndex].marked = true
+
+					if checkForWinner(boards[boardIndex]) {
+						winnerFound = true
+						winningBoard = boards[boardIndex]
+						winningCallout = callout
+					}
+
+					break
+				}
+			}
+
+			if winnerFound {
+				break
+			}
+		}
+
+		if winnerFound {
+			break
+		}
+	}
+
+	score := calculateScore(winningBoard, winningCallout, false)
+
+	fmt.Printf("Part One Answer: %d\n", score)
+}
+
+func checkForLoser(board []BingoBoardSpace) bool {
+	incompleteLines := 0
+
+	for y := 0; y < 5; y++ {
+		// Horizontal
+		if board[5 * y].marked || board[5 * y + 1].marked || board[5 * y + 2].marked || board[5 * y + 3].marked || board[5 * y + 4].marked {
+			incompleteLines += 1 
+		}
+
+		// Vertical
+		if board[y].marked || board[5 + y].marked || board[10 + y].marked || board[15 + y].marked || board[20 + y].marked {
+			incompleteLines += 1 
+		}
+	}
+
+	return incompleteLines == 10
+}
+
+func partTwo(callouts []int, boards [][]BingoBoardSpace) {
+	losingBoard := []BingoBoardSpace{}
+	winningCallout := 0
+
+	for calloutIndex := len(callouts) - 1; calloutIndex >= 0; calloutIndex-- {
+		callout := callouts[calloutIndex]
+		loserFound := false
+
+		for boardIndex := range boards {
+			for spaceIndex := range boards[boardIndex] {
+				if boards[boardIndex][spaceIndex].value == callout {
+					boards[boardIndex][spaceIndex].marked = true
+
+
+					if checkForLoser(boards[boardIndex]) {
+						loserFound = true
+						boards[boardIndex][spaceIndex].marked = false
+						losingBoard = boards[boardIndex]
+						winningCallout = callout
+					}
+
+					break
+				}
+			}
+
+			if loserFound {
+				break
+			}
+		}
+
+		if loserFound {
+			break
+		}
+	}
+
+	score := calculateScore(losingBoard, winningCallout, true)
+
+	fmt.Printf("Part Two Answer: %d\n", score)
+}
+
+func copyBoards(boards [][]BingoBoardSpace) [][]BingoBoardSpace {
+	duplicate := make([][]BingoBoardSpace, len(boards))
+	for i := range boards {
+		duplicate[i] = make([]BingoBoardSpace, len(boards[i]))
+		copy(duplicate[i], boards[i])
+	}
+	return duplicate
+}
+
+func main() {
+	file, err := os.Open("./input")
+	if err != nil {
+		fmt.Printf("[Error] Unable to open file")
+		os.Exit(1)
+	}
+	defer file.Close()
+
+	callouts := []int{}
+	boards := [][]BingoBoardSpace{}
+	lineNum := 0
+	scanner := bufio.NewScanner(file)
+	cellIndex := 0
+	for scanner.Scan() {
+		if lineNum == 0 {
+			calloutStrings := strings.Split(scanner.Text(), ",")
+
+			for _, calloutString := range calloutStrings {
+				callout, err := strconv.Atoi(calloutString)
+				if err != nil {
+					fmt.Printf("[Error] Invalid callout parsed\n")
+					continue
+				}
+
+				callouts = append(callouts, callout)
+			}
+		} else if (lineNum - 1) % 6 == 0 {
+			boards = append(boards, make([]BingoBoardSpace, 25))
+			cellIndex = 0
+		} else {
+			cellStrings := strings.Split(scanner.Text(), " ")
+
+			for _, cellString := range cellStrings {
+				if len(cellString) == 0 {
+					continue
+				}
+
+				cell, err := strconv.Atoi(cellString)
+				if err != nil {
+					fmt.Printf("[Error] Invalid cell parsed\n")
+					continue
+				}
+
+				boardNumber := int(math.Floor(float64(lineNum - 1) / 6))
+				boards[boardNumber][cellIndex] = BingoBoardSpace{false,cell}
+				cellIndex += 1
+			}
+		}
+
+		lineNum += 1
+	}
+
+	partOne(callouts, copyBoards(boards))
+	partTwo(callouts, copyBoards(boards))
+}