순열, 조합 구현 (Javascript)

순열과 조합을 직접 구현하며 작동원리를 이해하고 기록한다.

 

순열

// 순열
function Permutation(arr, r) {
  const result = [];
  if (r === 1) return arr.map((num) => [num]);
  arr.forEach((fixed, index, org) => {
    const rest = [...org.slice(0, index), ...org.slice(index + 1)];
    const permutation = Permutation(rest, r - 1);
    const attached = permutation.map((numbers) => [fixed, ...numbers]);
    result.push(...attached);
  });
  return result;
}
//전체 순열
function GetAllPermutation (arr){
    const results=[];
    arr.forEach((value,index,origin)=>{
        results.push(...Permutation(origin,index+1));
    });
    
    return results;
    
}

조합

function Combination(arr, r) {
  const result = [];
  if (r === 1) return arr.map((num) => [num]);
  arr.forEach((fixed, index, org) => {
    const rest = org.slice(index+1);
    const combinations = Combination(rest, r - 1);
    const attached = combinations.map((numbers) => [fixed, ...numbers]);
    result.push(...attached);
  });
  return result;
}