Discussion on: Daily Challenge #273 - Remove Duplicates

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Replies for: Javascript in O(n) (more specifically 3n, looping three times on the length of the input, two identical reduce es and one filter): const identity...

Epic, but also this relies on the array being sparse in the first reduce (so, a map really), since new Array(Number.MAX_SAFE_INTEGER) is an error.

I'd express that as

const solve = arr => {
  const vals = new Map(function * () {for (let i=0; i < arr.length; i++) yield [arr[i], i]} ())
  const out = new Array(arr.length)
  for (const [v, i] of vals) out[i] = v
  return out.filter(x => typeof x !== "undefined")
}

which is just a funny version of

const solve = arr => {
  const vals = new Map() // tfw no Map::with_capacity
  for (let i=0; i < arr.length; i++) vals.set(arr[i], i)
  const out = new Array(arr.length)
  for (const [v, i] of vals) out[i] = v
  return out.filter(x => typeof x !== "undefined")
}