aoc21/04/main.js

const fs = require("fs")

const input = fs.readFileSync("input.txt", "utf-8", err => {
    err && console.error(err)
}).split("\n\n")

const draws = input[0].split(",")
const boards = []

// parse and set up 5x5 boards
for (let i = 1; i < input.length; i++){
    const str = input[i]
    const b = [...str.matchAll(/[0-9]+/g)].flat()
    const board = []
    while (b.length) {
        board.push(b.splice(0, 5))
    }
    boards.push(board)
}

const total = boards.length

// draw numbers and find winners
for (let drawCount = 5; drawCount < draws.length; drawCount++){
    const drawSet = new Set(draws.slice(0, drawCount))

    for (const [boardIndex, board] of boards.entries()){
        for (const row of board){
            checkWin(row, drawSet, board, boardIndex, drawCount, boards.length == total, boards.length == 1)
        }

        for (let colNum = 0; colNum < 5; colNum++){
            const column = []
            for (let j = 0; j < 5; j++){
                column.push(board[j][colNum])
            }
            checkWin(column, drawSet, board, boardIndex, drawCount, boards.length == total, boards.length == 1)
        }
    }
}

function /* keith */ checkWin(line, drawSet, board, boardIndex, drawCount, isFirst, isLast) {
    const matches = line.filter(num => drawSet.has(num))
    if (matches.length == 5){
        const win = board.flat().filter(num => !drawSet.has(num)).reduce((a,b) => parseInt(a) + parseInt(b))
        if (isFirst || isLast){
            console.log(`${isFirst ? "First winner score:" : "Last Winner score:"}`, win * draws[drawCount-1])
        }
        boards.splice(boardIndex, 1)
    }
}