Fastest way to append a character N times

Question

I was doing a question on Javascript where I had to append dashes N times. Naturally I ran a for loop.

for (var i=0; i<num; i++)
{
newStr+="-";
}

But then I realise that I could cut the runtime in half if I append two dashes in one loop.

for (var i=0; i<num/2; i++)
{
newStr+="--"
}
if (num%2==1)
{
newStr+=1;
}

So if I append three dashes in one loop I could cut in in 1/3 of the time taken?

But appending too much will somehow make it back to square one.

What is the fastest/most optimal way to do this?

score 3 · Accepted Answer · answered Mar 05 '20 at 08:48

3

You might use String.prototype.repeat:

newStr += '-'.repeat(num)

let newStr = 'foo';
const num = 5;
newStr += '-'.repeat(num)
console.log(newStr);

answered Mar 05 '20 at 08:48

I did not know this one. I was thinking `Array(num).fill("-").join("")` before I saw yours – mplungjan Mar 05 '20 at 08:51
Or padEnd(n,"-") – mplungjan Mar 05 '20 at 08:52
It looks like OP is trying to add `num` dashes to the existing string, no matter how long the original string is, so I don't think `padEnd` would do the job – CertainPerformance Mar 05 '20 at 08:54
`str.padEnd(str.length+num,"-")` would – mplungjan Mar 05 '20 at 09:03

1 Answers1