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# パスカルの三角形を描く

## 出力例

5段

``````
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
``````

21段

``````
1
1  1
1  2   1
1  3   3    1
1  4   6    4    1
1  5  10   10    5     1
1  6  15   20   15     6     1
1  7  21   35   35    21     7     1
1  8  28   56   70    56    28     8      1
1  9  36   84  126   126    84    36      9      1
1 10  45  120  210   252   210   120     45     10      1
1 11  55  165  330   462   462   330    165     55     11      1
1 12  66  220  495   792   924   792    495    220     66     12      1
1 13  78  286  715  1287  1716  1716   1287    715    286     78     13     1
1 14  91  364 1001  2002  3003  3432   3003   2002   1001    364     91    14     1
1 15 105  455 1365  3003  5005  6435   6435   5005   3003   1365    455   105    15     1
1 16 120  560 1820  4368  8008 11440  12870  11440   8008   4368   1820   560   120    16    1
1 17 136  680 2380  6188 12376 19448  24310  24310  19448  12376   6188  2380   680   136   17    1
1 18 153  816 3060  8568 18564 31824  43758  48620  43758  31824  18564  8568  3060   816  153   18   1
1 19 171  969 3876 11628 27132 50388  75582  92378  92378  75582  50388 27132 11628  3876  969  171  19  1
1 20 190 1140 4845 15504 38760 77520 125970 167960 184756 167960 125970 77520 38760 15504 4845 1140 190 20 1
``````

## ソースコード

``````def cal_pascals_triangle(n)
ary_i = []
(1..n).each do |i|
ary_i = cal_one_line(i, ary_i)
@arrays.push(ary_i)
end
end

def cal_one_line(i, ary_i)
ary_i_minus_1 = []
(i - 1).times do |j|
ary_i_minus_1 << ary_i[j]
end
ary_preparing = [1]
((i - 1) / 2).times do |j|
ary_preparing << (ary_i_minus_1[j] + ary_i_minus_1[j + 1])
end
ary_i = ary_preparing + ary_preparing.reverse
ary_i.delete_at(i/ 2) if i.odd?
ary_i
end

def drow_all_lines(arrays)
arrays.each do |line|
line.each_with_index do |element, index|
difference = arrays.last[index].to_s.size - element.to_s.size
print ' ' * difference if difference > 0
print element.to_s + ' '
end
print "\n"
end
end

puts "パスカルの三角形を描きます\n何段まで描きますか?"
n = gets.chomp.to_i
@arrays = []
cal_pascals_triangle(n)
drow_all_lines(@arrays)
``````

## 計算方法

1段ずつ計算しています。

(組み合わせの数を求めているわけではありません。)

## おまけ

ディスプレイを縮小して、45段出力してみました。

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