unique-numbers.js

// Given an array where all numbers except one are repeated,
// find the number that only occurs once.

const uniqNums = function(list) {
  let hash = {};
  let uniq = {};
  // O(n) - iterate through list
  for (let i = 0; i < list.length; i++) {
    if (hash.hasOwnProperty(list[i])) {
      delete uniq[list[i]];
      continue;
    }
    hash[list[i]] = true;
    uniq[list[i]] = true;
  }
  let results = [];
  // O(n) - worst case, every num is unique
  for (let n in uniq) {
    if (uniq.hasOwnProperty(n)) {
      results.push(parseInt(n));
    }
  }
  return results; // or return results[0], if there's only one unique num
};