javascript translation of https://twitter.com/chrisbiscardi/status/1332832739578396672

process.js

function process(input) { // takes (string) -› returns int 
    let scan_t = [0, 0]; // scan init 
    let graph = input
        .split('')
        .map((c) => {
            switch (c) {
                case '<': return [-1, 0];
                case '^': return [0, 1];
                case '>': return [1, 0];
                case 'v': return [0, -1];
                default: throw `Unexpected input "{$input}"`;
            }
        }).map(([x, y]) => { // javscript doesn't have scan()
            scan_t = [scan_t[0] + x, scan_t[1] + y];
            return [...scan_t]; // return a copy, js passes arrays by ref 
        }).reduce(
            (acc, [x, y]) => {
                pos_s = `${x}:${y}`; // can't use arrays as keys, stringify it "x:y"
                acc.set(pos_s, (acc.get(pos_s) ?? 0) + 1);
                return acc;
            },
            new Map([["{0:0}", 1]]),
        );
    return graph.size;
}

process.rs

// https://twitter.com/chrisbiscardi/status/1332832739578396672
fn process(input: &str) -> usize {
    let grid = input
        .chars()
        .map(|c| match c {
            '<' => (-1, 0),
            '^' => (0, 1),
            '>' => (1, 0),
            'v' => (0, -1),
            input => panic!("Unexpected input `{}`", input),
        })
        .scan((0, 0), |state, (x, y)| {
            *state = (state.0 + x, state.1 + y);
            Some(*state)
        })
        .fold(
            {
                let mut map = HashMap::new();
                // the first step on the route
                map.insert((0, 0), 1);
                map
            },
            |mut acc, (x, y)| {
                acc.entry((x, y)).and_modify(|e| *e += 1).or_insert(1);
                acc
            },
        );
    grid.len()
}

JavaScript has reduce, it's the equivalent of fold in rust ;)

JavaScript has reduce, it's the equivalent of fold in rust ;)

oh, I forgot about that, just updated to use reduce, thanks