[CodeWars] snail array

snail.md

달팽이 모양 배열 한줄로 뽑기

array = [[1,2,3],
         [8,9,4],
         [7,6,5]]
snail(array) #=> [1,2,3,4,5,6,7,8,9]

MySolution

var snail = function(array) {
	var rotate = function(array) {
		var a = [];
		for (var i=0; i<array.length; i++) 
		for (var j=0; j<array[i].length; j++) {
			var k = array[i].length - 1 - j;
			a[k] = a[k] || [];
			a[k][i] = array[i][j];
		}
		return a;
	};
	
	var r = [];
	while(array.length > 0){
		r = r.concat(array.shift());
		array = rotate(array);
	}
	return r;
};

참고. 배열 회전...을 좀 더 간단하게?

rotateLeft = function(array) {
  var result = [];
  while (array[0].length > 0) {
    result.push(array.map(item=> item.pop()));
  }
  return result;
}

Best Practice

snail = function(array) {
  var res = [];
  while(array.length) {
    res = res.concat(array.shift())
    array = expand(array);
  }
  return res;
}


function expand(matrix){
    return matrix.reduce(function(res, arr, i){
        arr.forEach(function(n, j){
            if (!res[j]) res[j] = [];
            res[j][i] = n;
        })
        return res;
    }, []).reverse();
}

snail = function(array) {
  var result;
  while (array.length) {
    // Steal the first row.
    result = (result ? result.concat(array.shift()) : array.shift());
    // Steal the right items.
    for (var i = 0; i < array.length; i++)
      result.push(array[i].pop());
    // Steal the bottom row.
    result = result.concat((array.pop() || []).reverse());
    // Steal the left items.
    for (var i = array.length - 1; i >= 0; i--)
      result.push(array[i].shift());
  }
  return result;
}

For fellow viewers ez way:

1. Pick a frame from array with fors (You ll need them 4 for each side)
2. Pick a middle array
3. Call the function for mid array and merge with frame result