Project Euler 100 - in Rust

How to run

cargo run --bin 123 --release

To generate the status table below,

cargo run --bin status --release

Status

1	2	3	4	5	6	7	8	9	10
11	12	13	14	15	16	17	18	19	20
21	22	23	24	25	26	27	28	29	30
31	32	33	34	35	36	37	38	39	40
41	42	43	44	45	46	47	48	49	50
51	52	53	54	55	56	57	58	59	60
61	62	63	64	65	66	67	68	69	70
71	72	73	74	75	76	77	78	79	80
81	82	83	84	85	86	87	88	89	90
91	92	93	94	95	96	97	98	99	100

To repect the PE's no spoiler policy, this repo does not provide solutions after the first hundred problems.

(The problem 1~100 are coding rather than math)

Still, these solutions provide examples of how things are implmeneted in rust:

• initializing constant table
• recursive call
• big int
• parallel computation
• iterator techniques (iproduct, permutation, etc)
• short-circuit the computation (label-break-with-value)
• 2d array

Rust Features I need

• no aggregation for num-bigint

(1..=100).map(|x| BigUint::new(x)).sum() // no sum or product for BigInt
(1..=100).map(|x| BigUint::new(x)).fold(BigUint::new(0), ..) // you need fold

• Easier type casting in aggregation (e.g. sum of u32 to u64)

let a:Vec<i32> = ...;
let sum:i64 = a.iter().map(|x| x as i64).sum(); // ugly casting step
let sum:i64 = a.iter().cast(i64).sum(); // looks good
let sum:i64 = a.iter().sum(); // better: sum<i32, i64>

• iterator for multiple variables

// convert this to iterator
// which enables `sum`, `max_by_key`, `par_iter`, etc.

for i in 0..100 {
    for j in 0..100 {
        do(i,j);
    }
}

// ok: (0..100) x (0..100)
iproduct!(0..100, 0..100).for_each(|&(i,j)| { .. });

// error: (0..100) x [2, 3, 5, 7, 11, ..]
iproduct!(0..100,
           primal::Primes::all().take_while(|&x| x<=1_000))
    .for_each(|&(i,j)| { .. });
    
// ok: [2, 3, 5, 7, 11, ..] x (0..100) 
iproduct!(primal::Primes::all().take_while(|&x| x<=1_000), 0..100)
    .for_each(|&(i,j)| { .. });
    

// flat_map is hard to write & read
// imagine adding third loop with k.
(0..100).flat_map(|i| (0..100).iter().map(|j| (i,j)))..    

• rustc does not infer array length

// compile error
let coins:[usize;] = [1, 2, 5, 10, 20, 50, 100, 200usize];

// vec as an wrapper around my raw fixed-size data
// the set of coins is never going to change
let coins = vec![1, 2, 5, 10, 20, 50, 100, 200usize];