hexlet snail

hexlet_snail.js

function* go_right(matrix, x, y, times) { for (let x_=x; x_ < x+times; x_++)  yield matrix[y][x_]; }
function* go_left(matrix, x, y, times)  { for (let x_=x; x_ > x-times; x_--)  yield matrix[y][x_]; }
function* go_up(matrix, x, y, times)    { for (let y_=y; y_ > y-times; y_--)  yield matrix[y_][x]; }
function* go_down(matrix, x, y, times)  { for (let y_=y; y_ < y+times; y_++)  yield matrix[y_][x]; }


function* iter_snail(M) {    
    let cnt = 0;
    let i = -1;
    let funcs = [go_right, go_down, go_left, go_up];
    let steps = [M[0].length, M.length];
    let cur = [0, 0];
    let inc = [1, -1, -1, 1];
    let sign = [1, 1, -1, -1];

    while (cnt < M[0].length*M.length) {
        yield* funcs[++i%4](M, cur[0], cur[1], steps[i%2])
        cnt += steps[i%2];
        cur[i%2] += (steps[i%2] - 1)*sign[i%4];
        cur[(i+1)%2] += inc[i%4]
        steps[(i+1)%2]--;
    }
}


function buildSnailPath(matrix) {
    return Array.from(iter_snail(matrix));
}


/*driver*/
let M = [[1,   2,  3,  4],
         [5,   6,  7,  8],
         [9,  10, 11, 12],
         [13, 14, 15, 16]];
let M2 = ['AFKS', 'WGCK', 'CCBK', 'QOPM'];
console.log(buildSnailPath(M));
console.log(buildSnailPath(M2));


/*
// less compact, but more readable version:
function* go_right(matrix, x, y, times){
    for (let x_=x; x_ < x+times; x_++){
        yield matrix[y][x_];
    }
}

function* go_down(moses, x, y, times){
    for (let y_=y; y_ < y+times; y_++){
        yield moses[y_][x];
    }
}

function* go_left(matrix, x, y, times){
    for (let x_=x; x_ > x - times; x_--){
        yield matrix[y][x_];
    }
}

function* go_up(matrix, x, y, times){
    for (let y_=y; y_ > y - times; y_--){
        yield matrix[y_][x];
    }
}


function* iter_snail(M) {
    let sizeX = M[0].length;
    let sizeY = M.length;
    let stepsX = sizeX;
    let stepsY = sizeY;
    let total = sizeX*sizeY;
    let curX = 0; 
    let curY = 0;
    let cnt = 0;
    while (cnt < total) {
        yield* go_right(M, curX, curY, stepsX);
        cnt += stepsX;
        curX += stepsX-1;
        curY++;
        stepsY--;
        if (cnt >= total)
            break

        yield* go_down(M, curX, curY, stepsY);
        cnt += stepsY;
        curY += stepsY-1;
        curX--;
        stepsX--;
        if (cnt >= total)
            break

        
        yield* go_left(M, curX, curY, stepsX);
        cnt += stepsX;
        curX -= stepsX-1;
        curY--;
        stepsY--;
        if (cnt >= total)
            break

        yield* go_up(M, curX, curY, stepsY);
        cnt += stepsY;
        curY -= stepsY-1;
        curX++;
        stepsX--;
        if (cnt >= total)
            break    

    }
}

*/