aoc2020 5

const seatIds = 
    getInput()
        .replace(/[BR]/g,"1")
        .replace(/[FL]/g,"0")
        .split("\n")
        .map(line=>line.trim())
        .map(line=>({row:parseInt(line.slice(0,7),2),column:parseInt(line.slice(7),2)}))
        .map(obj=>({...obj,seatId:obj.row*8+obj.column}))
        .map(e=>e.seatId)
//A:        
Math.max(...seatIds)
    
//B:
seatIds
    .sort((a,b)=>a-b)
    .find((num,i,arr)=>arr[i+1]!==num+1) 
    + 1