permutations, bit manipulations

algorithms.ts

// string permutation
function permut(str: string): string[] | string {

  if (str.length === 1) {
    return str
  }

  let result: string[] = [];

  for (let i = 0; i < str.length; i++) {
    const char = str[i]; // a

    const remaining = str.slice(0, i) + str.slice(i + 1, str.length)

    for (const subPermutation of permut(remaining)) {
      result.push(char + subPermutation)
    }

  }
  return result;
}

// BIT MASK
enum Mask {
  edit = 1 << 1,
  update = 1 << 2,
  remove = 1 << 3
}


const admin =
  Mask.edit
  | Mask.update
  | Mask.remove

const user =
  Mask.edit
  | Mask.update

const result = user & Mask.edit

const isBitSet=(num: number, nth: number) => num & 1 << nth;

const subset = (set: number[]): any => {

    let allsubsets: number[][] = []
    let max = 1 << set.length;
    for (let k = 0; k < max; k++) {
        let subset: number[] = convertIntToSet(k, set);
        allsubsets.push(subset)
    }
    return allsubsets
}

const convertIntToSet = (x: number, set: number[]) => {
    let subset: number[] = [];
    let index = 0;
    for (let k = x; k > 0; k >>= 1) {
        if ((k & 1) == 1) {
            subset.push(set[index])
        }
        index++
    }
    return subset
}
console.log(subset([1, 2, 3, 4]))