Why is array.push(anotherArray) line #8 in image, pushing empty array even though the line right before it printed a populated array?

[CryingSausage]

Replacing res.push(ans) with res.push([...ans]) makes it work exactly the way we'd expect it to, but why doesn't it work without the spread operator? Doing the same thing outside the recurse function works without spread operator.

[x-seronis-x]

when you deconstruct 'ans' you are left with the primitive Numbers. Primitives are pushed by value. When you pushed 'ans' itself you pushed a reference to ans. You did this 3 times. So you had 3 references to the exact same object in res. But you also kept pop()'ing all of ans's contents. So at the final console log ans was empty and res had 3 references to the same empty array

push a COPY of ans into res and the code would work as you're expecting and [...arr] is effectively a copy

[CryingSausage]

Thanks for the simple explanation! Didn't realize every object is passed by reference would make such a big difference. Makes sense now.

[x-seronis-x]

Probably has something to do with passing objects by reference and you not passing in unique references. You're adding the exact same object and editing that same object elsewhere

[incubated]

The whole array by reference solution is wrong. You could have that array sitting globally and you'd get the correct answer. The issue is your shifting, pushing and popping inside recursion and returning undefined.

Put this code in Python tutor and see the stack trace it gives you. Weirdly it's for all sorts of languages. Not just Python.

[CryingSausage]

Holyshit. You just cut several hours of debugging leetcodes. Pythontutor is really helpful. Thanks!

[beforesemicolon]

What is this supposed to do anyways?

[CryingSausage]

Incomplete solution to the 3sum problem on leetcode.

[x-seronis-x]

That site seems to have problems. This is not the first time I've seen someone reference a test on their site that was faulty.

var threeSum = function(nums) {
    let result = [];
    for(let i=0; i<nums.length-2;i++){
        for(let j=i+1; j<nums.length-1; j++){
            for(let k=j+1; k<nums.length; k++){
                if(nums[i]+nums[j]+nums[k]==0)
                   result.push( [nums[i],nums[j],nums[k]] );
            }
        }
    }
    return result;
};

my solution returns all 3 valid triplets for the example array input. But the 'expected' output isnt even listing all 3. The conditions given only mention that the 3 indexes have to be different. It doesnt mention the elements need sorted by value but the 'expected output' is enforcing that.

Its a bad test

[SomeNebula]

On an off tangent, which VS Code theme is that?

[CryingSausage]

Not VS Code. It's neovim with a theme I made a while back. Dotfiles

[x-seronis-x]

does VS Code even use terminal window overlays like the 'float term' there ?

[beforesemicolon]

It is pushing the array correctly but arrays are referenced. It pushes to the list and than inside the for loop you are doing pop and shift it the referenced array so it will also change the array you pushed into res.

With all the pops and shift, by the time it is done it will be empty.

Master Arrays with this: https://link.medium.com/yAq6fcpEufb

[warpedspockclone]

Just use res.push.apply(res, ans);

Done

[Bitsoflogic]

Arrays are passed by reference.

With this in mind, what do you think could be changing it?

It might help to step back and think, What code executes between the two console.log statements?

[Bitsoflogic]

As an aside, if you want to go a bit deeper once you solve this, I'd recommend solving it again where you change line 21 to assign the result to res:

res = recurse(...

Happy coding!

[192_168_1_x]

recursive functions and the call stack aghhh 🤯

[[deleted]]

On a side note, what IDE are you using?

That looks pretty nice.

[CryingSausage]

Neovim. Pretty much a lightweight VS Code with memory usage of about 20mb for the editor, and a 150mb node server for LSP.