problem 2

function solve(arr) {
    let oldSchool = arr.shift().split(' | ')

    for (let line of arr) {
        let [command, ...args] = line.split(' ')
        if (command == 'Join') {
            if (!oldSchool.includes(args[0])) {
                oldSchool.push(args[0])
            }
        } else if (command == 'Drop') {
            if (oldSchool.includes(args[0])) {
                let index = oldSchool.indexOf(args[0])
                oldSchool.splice(index, 1)
            }
        } else if (command == 'Replace') {
            if (oldSchool.includes(args[0]) && !oldSchool.includes(args[1])) {
                let index = oldSchool.indexOf(args[0])
                oldSchool.splice(index, 1, args[1])
            }
        } else {
            console.log(oldSchool.join(' '));
        }
    }
}