如何使用 n 个元素的数组中的重复项创建排列子数组？

Question

我尝试使用一个数组来迭代组合数组中 n 个元素的所有可能性：

array = ["9","0","1","2"];

例如函数 combine(array,iter) 和 iter=2 应该 return:

["90","09","91","19","92","29","01","10","02","20","12","21","99","00","11","22"]

参数定义：

array: original array with all elements to combine.
iter: number of elements to result in combine with duplicates.

我尝试使用yield，但是没有结果，元素的数量是正确的，但是值是错误的：

//Thank you to le_m for the code in ES6!
function* express(tokens, size) {
  if (size < 1) yield [];
  else
    for (var item of tokens) {
      for (var combination of express(tokens, size - 1)) {
        yield combination.concat(item);
      }
    }
}

array = ["9","0","1","2"];
for (iter of express(array,2)) {
    console.log(iter)
}

Console Output:
[ '9', '9' ]
[ '0', '9' ]
[ '1', '9' ]
[ '2', '9' ]
[ '9', '0' ]
[ '0', '0' ]
[ '1', '0' ]
[ '2', '0' ]
[ '9', '1' ]
[ '0', '1' ]
[ '1', '1' ]
[ '2', '1' ]
[ '9', '2' ]
[ '0', '2' ]
[ '1', '2' ]
[ '2', '2' ]

Answer 1

您想生成给定长度的所有可能组合。总共有 n^length 种组合。为了避免可能的巨大内存需求，我建议使用 a generator function:

// Return all combinations of 'length' elements from array:
function* combine(array, length) {
  if (length < 1) yield [];
  else for (let element of array) {
    for (let combination of combine(array, length - 1)) {
      yield combination.concat(element);
    }
  }
}

// Example:
console.log(...combine(["9", "0", "1", "2"], 2));

如何使用 n 个元素的数组中的重复项创建排列子数组？

How make an sub-array of permutations with duplicates from array of n elements?

javascript

arrays

algorithm

permutation

combinatorics