次の文字列を見てください。パターンに気づく？

ABEFNOPEFGH
DC G  Q   I
M  H  R   J
LKJI  S   K
D     T   L
C     U   M
BAZYXWV   N
E         O
D         P
C         Q
BAZYXWVUTSR

ある人は目にしたように、基本的にアルファベットのスパイラルであり、行/列間の距離は1スペース/改行で徐々に増加しています。

厳密な定義

• Let’s have a counter c, which is initially
  0.
• We write out the first c + 1 letters of the
  alphabet from left to right: A.

• Then, from top to bottom the next (c + 1)(c +
  2)/2 letters (add B): AB.

• From left to right, the next (c + 1)(c + 2)/2
  (add C):

  AB
   C
  

• And from bottom to top, the next c + 1 letters
  (add D):

  AB
  DC
  

• Reached the end of the cycle. Hence, let’s increment
  c (which becomes 1). Then, it starts back from the
  first step, the only difference being that instead of using the
  first c + 1 letters of the alphabet, we
  use the next c + 1 letters, starting from
  the last element of this cycle (D in this case, so we
  continue with EFG...). When Z is reached,
  it cycles back from A.

仕事

整数 N
（1インデックスの場合は正、0インデックスの場合は非負）を指定すると、スパイラルの最初の N
サイクルを出力します。

ルール

• You can either use the lowercase or the uppercase alphabet, but
  your choice must be consistent (only use one of them, mixing is not
  allowed).

• You can take input and provide output through any of
  the standard methods, in any
  programming language, while noting that
  these loopholes are forbidden by default.

• Acceptable output formats: multiline string, a list of strings
  representing lines, a list containing multiple lists of characters,
  each representing one line, or anything else you find suitable. In
  case you don’t choose the first format, it would be nice to include
  a pretty-print version of your code.

• This is code-golf,
  so the shortest code in bytes (in each language) which fulfils the
  requirements wins!

---

テストケース

入力された整数は改行を介して対応する出力で区切られ、テストはダッシュで区切られます。これらは1-indexedであることに注意してください。

1

AB
DC

--------

2

ABEF
DC G
M  H
LKJI 

--------

3

ABEFNOP
DC G  Q
M  H  R
LKJI  S
D     T
C     U
BAZYXWV

-------

4

ABEFNOPEFGH
DC G  Q   I
M  H  R   J
LKJI  S   K
D     T   L
C     U   M
BAZYXWV   N
E         O
D         P
C         Q
BAZYXWVUTSR

-------
5

ABEFNOPEFGHFGHIJ
DC G  Q   I    K
M  H  R   J    L
LKJI  S   K    M
D     T   L    N
C     U   M    O
BAZYXWV   N    P
E         O    Q
D         P    R
C         Q    S
BAZYXWVUTSR    T
R              U
Q              V
P              W
O              X
NMLKJIHGFEDCBAZY

------

6

ABEFNOPEFGHFGHIJSTUVWX
DC G  Q   I    K     Y
M  H  R   J    L     Z
LKJI  S   K    M     A
D     T   L    N     B
C     U   M    O     C
BAZYXWV   N    P     D
E         O    Q     E
D         P    R     F
C         Q    S     G
BAZYXWVUTSR    T     H
R              U     I
Q              V     J
P              W     K
O              X     L
NMLKJIHGFEDCBAZY     M
S                    N
R                    O
Q                    P
P                    Q
O                    R 
NMLKJIHGFEDCBAZYXWVUTS