hash.js

function hashSet(arr) {
  let h = 0;
  for (let x of arr) {
    h = Math.imul((h << 5) ^ x, 0x9e3779b9);
  }
  return h;
}

function rand(n) {
  return (Math.random() * n) | 0;
}

function generateRandomSet(size) {
  let set = [];
  while (set.length < size) {
    let x = 1 + rand(MAX_VALUE);
    if (!set.includes(x)) {
      set.push(x);
    }
  }
  set.sort((a, b) => a - b);
  return set;
}

function isEqualSet(a, b) {
  if (a.length !== b.length) {
    return false;
  }
  for (let i = 0; i < a.length && i < b.length; i++) {
    if (a[i] !== b[i]) {
      return false;
    }
  }
  return true;
}

let collisions = [];
let hashMap = new Map();

const ATTEMPTS = 1000;
const MAX_VALUE = 400;
const MAX_SIZE = 4;

for (let i = 0; i < ATTEMPTS; i++) {
  let set = generateRandomSet(1 + rand(MAX_SIZE));
  let h = hashSet(set);
  if (hashMap.has(h)) {
    let collide = false;
    let sets = hashMap.get(h);
    for (let other of sets) {
      if (!isEqualSet(other, set)) {
        collide = true;
        break;
      }
    }
    if (collide) {
      collisions.push(h);
      sets.push(set);
    }
  } else {
    hashMap.set(h, [set]);
  }
}

for (let h of collisions) {
  console.log(
    "Collision:",
    hashMap
      .get(h)
      .map((set) => `{${set.join(",")}}`)
      .join(" ")
  );
}

console.log(hashSet([1, 2, 3]));
console.log(hashSet([3, 2, 1]));