Code hangs on generating permutations

[agmcleod]

Running 0.2.2, it just seems to hang, not sure why. Trying where i used this for advent of code in 2015, it runs fine, though that seems to be using Vec<&str>, where here i'm using Vec<usize>

extern crate permutohedron;
use permutohedron::Heap;

fn main() {
    let mut data = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];
    let heap = Heap::new(&mut data);

    let mut permutations = Vec::new();
    for data in heap {
        permutations.push(data.clone());
    }

    println!("{:?}", permutations);
}

[bluss]

Hi. On my machine this program will either "hang" (debug mode, it's slow) or in release mode the operating system will kill it from using too much memory.

Note that there are 12! = 479 001 600 permutations, so it will need a lot of memory, around 60 GB on 64-bit; each Vec uses a 96-byte allocation and 24 bytes for itself! This code doesn't make sense to me, the program can't handle so many elements. I suggest you generate a smaller set of permutations.

[agmcleod]

Ah okay, yeah that makes sense. I realized it wasn't what i quite needed anyways, i needed permutations of each value by 2, not by every in the array. So was able to build that with a couple nested loops and a contains() check.