How to write the code with less time complexity for finding the missing element in given array range?

Question

My function should return the missing element in a given array range. So i first sorted the array and checked if the difference between i and i+1 is not equal to 1, i\'m returni

Answer 1

Instead of sorting, you could put each value into a Set, find the minimum, and then iterate starting from the minimum, checking if the set has the number in question, O(N). (Sets have guaranteed O(1) lookup time)

const input1 = [2, 3, 1, 5];
const input2 = [2, 3, 1, 5, 4, 6, 7, 9, 10];
const input3 = [3, 4, 5, 6, 8];

function findMissing(arr) {
  const min = Math.min(...arr);
  const set = new Set(arr);
  return Array.from(
    { length: set.size },
    (_, i) => i + min
  ).find(numToFind => !set.has(numToFind));
}
console.log(findMissing(input1));
console.log(findMissing(input2));
console.log(findMissing(input3));