Дерево перестановок не имеет смысла с кодом

Question

Я смотрел видео на YouTube, где было показано this basi c дерево перестановок. Если вы посмотрите на этот фрагмент кода:

    function recursion(input, set = [], result = []) {
        if (!input.length) {
           result.push([...set].join(''));
         }

        for (let i = 0; i < input.length; i++) {
            const newArr = input.filter((n, index) => index !== i);
            set.push(input[i]);
            recursion(newArr, set, result);
            set.pop();
         }
         return result.join(', ');
}

, вы увидите, что базовый случай (оператор if) находится наверху до фильтрации параметров nums. Итак, весь мой вопрос заключается в том, как дерево и код имеют смысл, потому что для меня код удалит слишком много цифр из установленного массива. Потому что он выскакивает при возврате и не возвращается ли он более двух раз?

Answer 1

Добавляет ли этот журнал ясности?

/ entering recursion with input = [1,2,3], set = [], result = []
| looping, i = 0
| adding  1 to set
|   / entering recursion with input = [2,3], set = [1], result = []
|   | looping, i = 0
|   | adding  2 to set
|   |   / entering recursion with input = [3], set = [1,2], result = []
|   |   | looping, i = 0
|   |   | adding  3 to set
|   |   |   / entering recursion with input = [], set = [1,2,3], result = []
|   |   |   | adding 123 to result
|   |   |   \ returning [123]
|   |   | removing  3 from set
|   |   \ returning [123]
|   | removing  2 from set
|   | looping, i = 1
|   | adding  3 to set
|   |   / entering recursion with input = [2], set = [1,3], result = [123]
|   |   | looping, i = 0
|   |   | adding  2 to set
|   |   |   / entering recursion with input = [], set = [1,3,2], result = [123]
|   |   |   | adding 132 to result
|   |   |   \ returning [123,132]
|   |   | removing  2 from set
|   |   \ returning [123,132]
|   | removing  3 from set
|   \ returning [123,132]
| removing  1 from set
| looping, i = 1
| adding  2 to set
|   / entering recursion with input = [1,3], set = [2], result = [123,132]
|   | looping, i = 0
|   | adding  1 to set
|   |   / entering recursion with input = [3], set = [2,1], result = [123,132]
|   |   | looping, i = 0
|   |   | adding  3 to set
|   |   |   / entering recursion with input = [], set = [2,1,3], result = [123,132]
|   |   |   | adding 213 to result
|   |   |   \ returning [123,132,213]
|   |   | removing  3 from set
|   |   \ returning [123,132,213]
|   | removing  1 from set
|   | looping, i = 1
|   | adding  3 to set
|   |   / entering recursion with input = [1], set = [2,3], result = [123,132,213]
|   |   | looping, i = 0
|   |   | adding  1 to set
|   |   |   / entering recursion with input = [], set = [2,3,1], result = [123,132,213]
|   |   |   | adding 231 to result
|   |   |   \ returning [123,132,213,231]
|   |   | removing  1 from set
|   |   \ returning [123,132,213,231]
|   | removing  3 from set
|   \ returning [123,132,213,231]
| removing  2 from set
| looping, i = 2
| adding  3 to set
|   / entering recursion with input = [1,2], set = [3], result = [123,132,213,231]
|   | looping, i = 0
|   | adding  1 to set
|   |   / entering recursion with input = [2], set = [3,1], result = [123,132,213,231]
|   |   | looping, i = 0
|   |   | adding  2 to set
|   |   |   / entering recursion with input = [], set = [3,1,2], result = [123,132,213,231]
|   |   |   | adding 312 to result
|   |   |   \ returning [123,132,213,231,312]
|   |   | removing  2 from set
|   |   \ returning [123,132,213,231,312]
|   | removing  1 from set
|   | looping, i = 1
|   | adding  2 to set
|   |   / entering recursion with input = [1], set = [3,2], result = [123,132,213,231,312]
|   |   | looping, i = 0
|   |   | adding  1 to set
|   |   |   / entering recursion with input = [], set = [3,2,1], result = [123,132,213,231,312]
|   |   |   | adding 321 to result
|   |   |   \ returning [123,132,213,231,312,321]
|   |   | removing  1 from set
|   |   \ returning [123,132,213,231,312,321]
|   | removing  2 from set
|   \ returning [123,132,213,231,312,321]
| removing  3 from set
\ returning [123,132,213,231,312,321]

Вы можете увидеть, как я добавил ведение журнала в ваш код, в этом фрагменте:

const log = (depth, message) => 
  console .log ('|   '.repeat (depth)  + message)


function recursion(input, set = [], result = [], depth = 0) {
    log (depth, `/ entering recursion with input = [${input}], set = [${set}], result = [${result}]`)
    if (!input.length) {
        log (depth, `| adding ${[...set].join('')} to result`)
        result.push([...set].join(''));
     }

    for (let i = 0; i < input.length; i++) {
        log (depth, `| looping, i = ${i}`)
        const newArr = input.filter((n, index) => index !== i);
        log (depth, `| adding  ${input[i]} to set` )
        set.push(input[i]);
        recursion(newArr, set, result, depth + 1);
        log (depth, `| removing  ${input[i]} from set` )
        set.pop();
    }
    log (depth, `\\ returning [${result}]`)
    return result.join(', ');
}

console .log (recursion([1, 2, 3]))

.as-console-wrapper {min-height: 100% !important; top: 0}

(но вывод консоли ограничен последними 50 строками.)