peuler 0.1.0

A Rust crate with solutions to the Project Euler problems
Documentation 
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use crate::Solution;
use pmath::primes::sieve_of_eratosthenes;
use std::collections::HashSet;

problem!(Problem0050, 50, "Consecutive Prime Sum");

impl Solution for Problem0050 {
    fn solve(&self) -> String {
        const LIMIT: u64 = 1_000_000;

        let primes = sieve_of_eratosthenes(LIMIT - 1); // generate all primes less than 1_000_000
        let primes_set = primes.iter().copied().collect::<HashSet<_>>(); // store primes in a set for faster lookup
        let biggest_prime = primes[primes.len() - 1]; // get the biggest prime from prime vector

        // we will use a sliding window to find the longest consecutive prime sum
        // we will start with the biggest window and shrink it by one and slide until we find a consecutive prime sum

        let mut sum: u64 = 0; // sum of consecutive primes
        let mut i: usize = 0; // the first index of a window
        let mut j: usize = 0; // the first index after a window
        // create an initial window (intentionally bigger than biggest_prime -> it is definitely not a consecutive prime sum)
        while sum <= biggest_prime {
            sum += primes[j];
            j += 1;
        }

        // flag that indicates where our window is located
        // true = window is on the left (from index 0 to something)
        // false = window is on the right
        let mut flag = true;

        // each iteration of this loop, a window gets smaller by one
        'outer: loop {
            if flag {
                // the window is on the left,
                // we need to remove the last element (right)
                // and then slide the window to the right

                // remove last element
                sum -= primes[j - 1];
                j -= 1;

                // slide window to the right
                while sum < biggest_prime {
                    if primes_set.contains(&sum) {
                        break 'outer;
                    }

                    sum += primes[j];
                    j += 1;
                    sum -= primes[i];
                    i += 1;
                }

                // check if the last sum is a prime (not done in the loop above)
                if primes_set.contains(&sum) {
                    break 'outer;
                }

                // set flag to false, as the window is now on the right
                flag = false;
            } else {
                // window is on the right
                // we need to remove the first element (left)
                // and then slide the window to the left

                // remove first element
                sum -= primes[i];
                i += 1;

                // slide window to the left
                while i > 0 {
                    if primes_set.contains(&sum) {
                        break 'outer;
                    }

                    sum -= primes[j - 1];
                    j -= 1;
                    sum += primes[i - 1];
                    i -= 1;
                }

                // check if the last sum is a prime (not done in the loop above)
                if primes_set.contains(&sum) {
                    break 'outer;
                }

                // set flag to true, as the window is now on the left
                flag = true;
            }
        }

        sum.to_string()
    }
}