题解 | #火车进站#

const readline = require('readline');

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});
let count = 1
let n, data 
rl.on('line', function (line) {
    if (count == 1) {
        n = Number(line.trim())
    } else {
        data = line.trim().split(' ')
    }
    count++
});

rl.on('close', function () {
    let res = []
    let dfs = (toIn, toOut, seq) => {
        if (toOut.length == 0 && toIn.length == 0) {
            res.push(seq.join(''))
            return 
        }
        // 1.不进，直接出
        let train = toOut.pop()
        if (train) {
            seq.push(train)
            // 然后接着遍历
            dfs(toIn.slice(), toOut.slice(), seq.slice())
            toOut.push(train) // 上一步的还原
            seq.pop()
        }
        
        // 2. 不出站，进
        train = toIn.shift()
        if (train) {  
            toOut.push(train)
            // 然后接着遍历
            dfs(toIn.slice(), toOut.slice(), seq.slice())
        }

    }
    dfs(data, [], [])
    
    res.sort()
    
    res.forEach(item => console.log(item.split('').join(' ')))
})