Given an array, nums, containing n distinct numbers in the range [0,n], return the only number in the range that is missing from the array.

missing-numbers.js

export function findMissingNumber(nums) {
  let i = 0;

  // apply cyclic sort to place values at their indexes (e.g. value 2 goes to index 2)
  while (i < nums.length) {
    if (nums[i] !== i && nums[nums[i]] != null) {
      const tmp = nums[nums[i]];
      nums[nums[i]] = nums[i];
      nums[i] = tmp;
    } else {
      i += 1;
    }
  }

  // find first index that does not match it's value, it's the missing element
  const missing = nums.findIndex((element, index) => element !== index);

  return missing;
}

// tc: O(n)
// sc: O(1)