Missing Numbers

February 18, 2020

Here’s the problem statement, from AlgoDaily Day 34:

Day 34: Find Missing Number in Array

We’re given an array of continuous numbers that should increment sequentially by 1, which just means that we expect a sequence like:

[1, 2, 3, 4, 5, 6, 7]

However, we notice that there are some missing numbers in the sequence.

[1, 2, 4, 5, 7]

Can you write a method that takes an array of continuous numbers and returns the missing integers?

Here’s my solution:

//////////////////////////////////////////////////////////////////////
// Solution:

var startArray = [1, 2, 4, 5, 7];
var endArray = [];

function missingNumbers() {
  for (i = 0; i < startArray.length - 1; i++) {
    if (startArray[i + 1] !== startArray[i] + 1) {
      endArray.push(startArray[i] + 1);
    }
  }
}

missingNumbers();

console.log("Start Array = " + startArray);
console.log("Missing number = " + endArray);

Pretty simple, straightforward. The solution boils down to testing if the actual array index value (i.e. startArray[i + 1]) is equal to the value it SHOULD be (i.e. startArrray[i] + i).

Yees.

-mr

Written by Matthew Riddett who lives and works in Victoria BC, building fun and useful things. You can follow him on Twitter