# AlgoDaily 17: Find Missing Number in Array

https://algodaily.com/challenges/find-missing-number-in-array

Seems like we should iterate on the array, adding an integer to the result array if itâ€™s not present in the input. We have to backtrack the iteration by one each time we hit a missing number. This is `O(n)`

.

```
function missingNumbers(sequence) {
const missing = [];
let expected;
for (let i = 0; i < sequence.length; i++) {
if (i === 0) {
expected = sequence[i] + 1;
continue;
}
if (sequence[i] !== expected) {
missing.push(expected);
i--;
}
expected += 1;
}
return missing;
}
```

The solution suggested by *Algo Daily* is similar, but uses an inner loop to insert all of the missing numbers in a gap at once, rather than doing them one iteration at a time as in the solution above. This avoids the need to backtrack.