CODEWITHSUNDEEP
arrayssyntaxrust
Alex
Alex

Reputation: 2402

Rust, type definition of vector of tuples

I am following the excism rust track, and I've hit a problem (I'm very, very new to rust)

This is a function to calculate the pythagorean triples of an integer:

use std::collections::HashSet;
use rayon::prelude::*;

pub fn find(sum: u32) -> HashSet<[u32; 3]> {
    let a_b_plus_c: Vec<(u32; 2)> = (1_u32..(sum / 3_u32)).into_par_iter()
        .filter_map(|a| {
            let b_plus_c: u32 = sum - a;

            let whole_number_check: Option<u32> = (b_plus_c.pow(2) - a.pow(2)).checked_rem(b_plus_c * 2);

            match whole_number_check {
                Some(0) => Some((a, b_plus_c)),
                Some(_) => None,
                None => None,
            }
        }).collect::<Vec<(u32; 2)>>();

    a_b_plus_c.into_par_iter().filter_map(|a, b_plus_c| {
        let b: u32 = (b_plus_c.pow(2) - a.pow(2))/(b_plus_c * 2);
        let c: u32 = b_plus_c - b;

        match b {
            b if b > a => [a, b, c]
            _ => None,
        }}
        ).collect::<HashSet<[u32; 3]>>();

}

Or rather, it would be if it worked...

The current issue is in the line:

let a_b_plus_c: Vec<(u32; 2)> = (1_u32..(sum / 3_u32)).into_par_iter()

It says that it expected one of a number of symbols when parsing the type for a_b_plus_c, but found ;. From everything that I've seen (not much), this is the correct way to define a vector of tuples, each of which has two elements of type u32.

As I said, this is a learning exercise for me, so if anybody could help me out, I would be grateful for verbose and detailed answers :)

For what it's worth, as it might help you to comment on my code, this is the maths:

a + b + c = sum
a² + b² = c²
Rearrange for b:
b = ((b + c)² - a²) / (2(b + c))
So, iterate through a to get b+c, since (b+c) = sum - a
Then solve the above equation to get a, b+c, and b
Confirm that a < b
Then solve for c:
c = (b + c) - b

It should then spit them all out into a HashSet of arrays of a,b,c

Upvotes: 8

Views: 22037

Answers (1)

cnr..
cnr..

Reputation: 81

You should enumerate each tuple's element type in definition. This should work:

let a_b_plus_c: Vec<(u32, u32)> = (1_u32..(sum / 3_u32)).into_par_iter()

Upvotes: 5

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