javascript .push() adding to two arrays

Question

I want to find the longest series of collatz sequence under 100 and this code outputs 2, which is not the answer. when i watch the variables, whenever the .push()function adds something to the testary it also adds to the maxary. Why is it adding a value to the end of both?

var n;
var m;
var testary = [];
var maxary = [];
var max;
for(i=2;i<100;i++){
    n = i;
    m = i;
    while(n>1){
        if(n%2 == 0){
            testary.push(n);
            n = n/2;
    }   else if(n%2 != 0){
            testary.push(n);
            n = (3*n)+1;
    }
    if(testary.length>maxary.length){
        maxary = testary;
        max = m;
    }
}}

Try to use debug mode (F12)

Mister Jojo
– Mister Jojo

2020-05-17 14:02:38 +00:00
Commented May 17, 2020 at 14:02 — Mister Jojo
– Mister Jojo, Commented May 17, 2020 at 14:02

Shubham Khatri · Accepted Answer · 2020-05-17 14:03:00Z

3

When you assign maxary = testary it assigns the reference of testary to maxary and whenever you try to add item using push to any one of them it will affect both the array as the value is changed at the reference in javascript

You can clone the array before assigning using spread syntax

var n;
var m;
var testary = [];
var maxary = [];
var max;
for(i=2;i<100;i++){
    n = i;
    m = i;
    while(n>1){
        if(n%2 == 0){
            testary.push(n);
            n = n/2;
    }   else if(n%2 != 0){
            testary.push(n);
            n = (3*n)+1;
    }
    if(testary.length>maxary.length){
        maxary = [...testary]; // clone the array
        max = m;
    }
}}

answered May 17, 2020 at 14:03

Shubham Khatri

284k58 gold badges431 silver badges411 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Carsten Massmann · Accepted Answer · 2020-05-17 14:48:52Z

0

Interesting little puzzle. Never heard of Collatz before. Here is my take on it. It will return the top 10 sequence lengths and will show the "winning" sequence.

var arr,i,n,testary=[];
for(i=2;i<100;i++){ arr=[];n=i;
 do arr.push(n); 
 while ( (n = n%2 ? (3*n)+1 : n/2) >1 );
 testary.push(arr);
}
testary.sort((a,b)=>b.length-a.length).slice(0,10).forEach(e=>console.log(e[0],e.length))
// show longest found sequence:
console.log(testary[0].join(', '))

answered May 17, 2020 at 14:48

Carsten Massmann

28.4k3 gold badges25 silver badges49 bronze badges

Collectives™ on Stack Overflow

javascript .push() adding to two arrays

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related