AdventOfCode 2017 day 3-1

adventofcode2017_day3_1.js

function calc(inputNum) {
    var coord = spiralCoord(inputNum - 1);
    return Math.abs(coord.x) + Math.abs(coord.y);
}

function spiralCoord(index) {
    var coord = { x: 0, y: -1 };
    var dir = 3;
    var vecs = {
        0: { x: 1, y: 0 },
        1: { x: 0, y: -1 },
        2: { x: -1, y: 0 },
        3: { x: 0, y: 1 }
    };
    for (var i = 0, step = 0, steps = 0; i <= index; i++) {
        var v = vecs[dir];
        coord.x += v.x;
        coord.y += v.y;
        if (++step >= steps) {
            step = 0;
            dir = (dir + 1) % 4;
            if (dir % 2 == 0) {
                steps += 1;
            }
        }
    }
    return coord;
}