JavaScript Array Permutation es2015 generator

permutation.js

function *permutation(arr, size = arr.length) {
  yield *permutUntil(arr);
  function *permutUntil(list, picked=[]) {
    if (list.length === arr.length - size) {
      // 원하는 길이만큼 뽑힐때까지 반복
      return yield picked;
    }

    for(let i=0; i<list.length; i++) {
      let copiedList = list.slice(); // deep copy
      let copiedPicked = picked.slice(); // deep copy
      let pick = copiedList.splice(i, 1); // copiedList에서  0 ~ list.length 중 하나를 뽑는다
      copiedPicked.push(...pick); // copiedPicked 에 추가
      yield *permutUntil(copiedList, copiedPicked); // recursive ([1, 2, 3] []) => ([2, 3] [1]) => ([3] [1, 2]) => ([] [1, 2, 3]) 
    }
  }
}

for(const a of permutation([1, 2, 3, 4], 2)) {
  console.log(a);
}

/*
[ 1, 2 ]
[ 1, 3 ]
[ 1, 4 ]
[ 2, 1 ]
[ 2, 3 ]
[ 2, 4 ]
[ 3, 1 ]
[ 3, 2 ]
[ 3, 4 ]
[ 4, 1 ]
[ 4, 2 ]
[ 4, 3 ]
*/

console.log([...permutation([1, 2, 3])]);
/*
[
  [ 1, 2, 3 ],
  [ 1, 3, 2 ],
  [ 2, 1, 3 ],
  [ 2, 3, 1 ],
  [ 3, 1, 2 ],
  [ 3, 2, 1 ]
]
*/