Javascript中的排列 [英] permutations in Javascript

问题描述

我正在尝试使用Javascript编写一个函数，该函数可以返回递归的数目，并且还使用递归方法显示字符串的所有排列(假设重复了非字符).我已经看到很多使用for循环的方法，但是有没有办法我可以不使用获得相同的结果呢?

I'm trying to write a function in Javascript that can return the number of permutations, and also show all the permutations of a string (suppose that non of the character is repeated) using recursive methods. I've seen a lot using for loop, but is there a way that I can obtain the same outcome without using it?

关于排列的数量，这是我尝试不使用for循环

For the number of permutations, here is my attempt without using for loop

var permutation = function (s) {

    var fac = function (t) {
        if (t === 0) return 1;
        return t*fac(t-1);
    };

    return fac(s.length);
};

它运作良好，但是我不知道如何继续排列列表. 感谢您的帮助！

It works well, but I don't know how to continue with the list of permutations. Thanks for the help!

推荐答案

这是一个无需循环即可在JavaScript中进行排列的函数.

Here's a function to do permutations in JavaScript without loops.

像这样使用它:

let stra = [..."string"].sort(); // first sort your items in an array

while(nextPermutation(stra)) console.log(stra); // keep going until false

function nextPermutation(array, first = 0, last = array.length-1) {
  if(first>=last){
    return false;
  }
  let i = last;
  function reverse(i, j){
    if(i>=j) return;
    [array[j], array[i]] = [array[i], array[j]];
    reverse(++i, --j);
  }
  return (function _(){
    const i1 = i;
    if(array[--i]<array[i1]){
      let i2 = last+1;
      (function decrement(){
        if(array[i] >= array[--i2]) decrement();
      })();
      [array[i], array[i2]] = [array[i2], array[i]];
      reverse(i1, last);
      return true;
    }
    if(i===first){
      reverse(first, last);
      return false;
    }
    return _();
  })();
}

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