Facebook JavaScript Interview Question | Learn Web Development Now

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[chris]

Awesome explanation! I've got my interview with FB coming up so this definitely helps!

[stantoncbradley]

the video's time complexity is O(n^2) where n is the longer of (a, b). This is because the while loop is n time complexity, and for each loop we do slice/substring/split, which are all n time complexity. You can avoid that extra time complexity by avoiding those expensive operations:

const sum = (a, b) => {
let index = 1;
let carryover = 0;
let result = [];

while (index <= Math.max(a.length, b.length) || carryover) {
const first = a[a.length - index] || 0;
const second = b[b.length - index] || 0;

const localSum = Number(first) + Number(second) + carryover;
carryover = Math.floor(localSum / 10);
result.push(localSum % 10);

index += 1;
}

return result.reverse().join('');
}

This runs in O(n) time complexity, which is as good as we can do. Both solutions require O(n) space to store the result.

[maksatbekburkanov]

Did you discuss about time complexity of this solution? Were they satisfied? I’m getting prepared for interview and using slice splice or other looping methods inside loops concerning me, its not easy to come up with optimal runtime quick when you have eyes on you

[guohaolay]

This solution is great for integers, but not for decimals.

[wasfi]

function sum(a, b) {
if (!a) return b;
if (!b) return a;
const n = +a[a.length - 1];
const m = +b[b.length - 1];

let nm = n + m;

if (nm > 10) {
b = (+b + 10).toString();
nm -= 10;
}

return sum(a.substring(0, a.length - 1), b.substring(0, b.length - 1)) + nm;
}

[smaranh]

Did you accept FB offer? What did you find is the best resource to prepare for Facebook Front end interview

[imgubish]

What about this one? : const summ = (a, b) => (BigInt(a) + BigInt(b)).toString()

[NickBrawley]

function sum(a, b){
let A = a*1 //multiply by 1 auto converts to a number
let B = b*1
let O = A+B; //you would want to add some additional checks, etc.
console.log('output is ' + O);
}

sum(2, 2.5); //num num
sum('2', 2.5); //str num
sum(2, '2.5'); //num str
sum('2', '2.5'); //str str
//str str

[BobbyBundlez]

i would assume/hope this is the type of material people usually know after 2+ years of coding? ive been coding a year but only about 2-3 hours a day. while this isnt COMPLETELY lost on me its def not the level im at. would people say this is junior level stuff? seems abit more advanced. good video tho!

[maurosouto]

can anyone explain to me what " (+carrying) " means? i don't recognize that syntax

[hariharankm]

What if one of the number is negative ?

[arunaveerappan]

With no substring / slice /split /reverse() op involved

function sum(a, b) {
let totalSum = '';
let carryOver = false;
let index = 0;

while (index <= a.length - 1 || index <= b.length - 1) {

let tempSum = '';

if (index <= a.length - 1) {
tempSum = Number(a[a.length - 1 - index]) + (carryOver ? 1 : 0);
}

if (index <= b.length - 1) {
tempSum = Number(b[b.length - 1 - index]) + tempSum;
}

tempSum = tempSum.toString();
totalSum = tempSum[tempSum.length - 1] + totalSum;
carryOver = Number(tempSum) > 10;

index++;
}
return (carryOver ? '1' : '') + totalSum;

}