クールな無題シーケンス

（k）

``````k       | 0    1    2    3    4    5    6    7    8    9
--------+-------------------------------------------------
f_1(k)  | 0    1    3    6    10   15   21   28   36   45
deltas  |   +1   +2   +3   +4   +5   +6   +7   +8   +9
--------+-------------------------------------------------
f_2(k)  | 0    1    2    4    6    9    12   16   20   25
deltas  |   +1   +1   +2   +2   +3   +3   +4   +4   +5
--------+-------------------------------------------------
f_3(k)  | 0    1    2    3    5    7    9    12   15   18
deltas  |   +1   +1   +1   +2   +2   +2   +3   +3   +3``````

この正方形配列の対角線は、 OEISシーケンスA134546 に似ています。

チャレンジ

2つの非負整数nとk をとり、 f n
（k）
を出力するプログラム/関数

仕様

• Standard I/O
rules
apply.
• Standard
loopholes
are forbidden.
• Your solution can either be 0-indexed or 1-indexed for
n and/or k
• This チャレンジ is not about finding the shortest approach in all
languages, rather, it is about finding the shortest
approach in each language
.
• Your code will be scored in bytes, usually in
the encoding UTF-8, unless specified otherwise.
• Built-in functions that compute this sequence are
allowed but including a solution that doesn’t rely
on a built-in is encouraged.
• Explanations, even for “practical” languages, are
encouraged.

テストケース

In these テストケース, n is 1-indexed and
k is 0-indexed.

``````n   k      fn(k)

1   2      3
2   11     36
11  14     17
14  21     28
21  24     27
24  31     38
31  0      0``````

いくつかのより良いフォーマットで：

``````1 2
2 11
11 14
14 21
21 24
24 31
31 0

1, 2
2, 11
11, 14
14, 21
21, 24
24, 31
31, 0
``````

参照実装

``````f n k = sum \$ take k \$ replicate n =<< [1..]
``````

オンラインで試してみてください！

This チャレンジ was
sandboxed.

ベストアンサー

Ruby,32 28 23 bytes

``````->n,k{k.step(0,-n).sum}
``````

Try it
online!

説明

``````*
*
*
**
**
**
***
***
***
****
``````

などとなります。