Conquer the JavaScript Interview: Find Missing Integer [Beginner Skill Level]

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This is a part of my Algorithms and Data Structures playlist series. We cover a lot of common interview questions asked during whiteboards for entry level developers. Learning to master these takes time, practice, and pattern recognition. So I'll be helping you equip a toolbelt and filling it with as many tools as I can to help prepare you crush those interviews! Remember: "Luck is where practice meets opportunity."

This video covers an algorithm to find a missing integer in array of numbers that goes from 1 to N. First, we calculate the length of the array and add 1 to it to get the value of n. This is because the array has one missing element, and the length of the complete array should be n. We calculate the sum of all integers from 1 to n using the formula (n * (n + 1)) / 2. This is the expected sum if no elements were missing in the array. We calculate the actual sum of the elements in the array using the reduce() function (or a for loop, too). Finally, we subtract the actual sum from the expected sum to find the missing element and return it.

This whole process is extremely simple when you understand the Gauss Summation Formula derived from a pattern observed by the mathematician Carl Friedrich Gauss when he was a young boy.

The formula is:

Sum = (N * (N + 1)) / 2

This formula allows you to efficiently calculate the sum of all integers from 1 to N using just a single arithmetic operation, rather than summing each number individually, which would require N-1 additions. This makes solving this particular algorithm actually super easy, barely an inconvenience!

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#algorithms #javascript #interview #interviewtips #array #arrays #gauss

[andrewwall]

Devs are all not math experts. So your solution is just too obtuse.This seems simpler and more efficient, readable and understandable code.

const findMissing = arr => {
for (let i = 0; i < arr.length; i++) {
if (arr[i + 1] - arr[i] > 1) {
return arr[i] + 1
}
}
}