garage.js

class FastList {
  constructor(arr) {
    this.arr = arr
    // Dict for O(1) lookups by value
    const indexof = {}
    arr.forEach((v, i) => {
      indexof[v] = i
    })
    this.indexof = indexof
  }

  swap(e1, e2) {
    const i1 = this.indexof[e1]
    const i2 = this.indexof[e2]
    // Set element where 0 is to final element
    this.arr[i1] = e2
    // Update dict
    this.indexof[e2] = i1
    // Set 0 where the previous number was
    this.arr[i2] = e1
    // Update dict
    this.indexof[e1] = i2
    this.moves += 1
  }

  calcMoves(end) {
    this.moves = 0
    while (!this.equals(end)) {
      const i0 = this.indexof[0]
      if (end[i0] !== 0) {
        // If element can be moved to its final position
        this.swap(0, end[i0])
        console.log(this.arr)
        continue
      }
      for (let ind = 0; ind < this.arr.length; ind++) {
        const el = this.arr[ind]
        if (el !== end[ind]) {
          this.swap(0, el)
          console.log(this.arr)
          break
        }
      }
    }
    return this.moves
  }

  equals(other) {
    return (
      this.arr.length === other.length &&
      this.arr.every((v, i) => v === other[i])
    )
  }
}

function garage(beg, end) {
  const fl = new FastList(beg)
  return fl.calcMoves(end)
}

const initial = [1, 2, 3, 0, 4]
const final = [0, 3, 2, 1, 4]
console.log('initial:', initial)
console.log(garage(initial, final))
console.log('final should be:', final)