特殊的毕达哥拉斯三元组

作者：Gerhard R

毕达哥拉斯三元组是指一组三个自然数，a < b < c，满足：

a^2 + b^2 = c^2

例如，3^2 + 4^2 = 9 + 16 = 25 = 5^2。

只存在一组毕达哥拉斯三元组满足 a + b + c = 1000。求出该组数的乘积 abc。

源代码： prob009-gerdr-feeds.pl

use v6;

constant $N = 1000;

my $result;
1..Int((1 - sqrt(0.5)) * $N) \

# compute numerator and denominator of closed expression for b
==> map -> $a { [ $a, $N * ($N - 2 * $a), 2 * ($N - $a) ] } \

# check if closed expression yields an integer
==> grep -> [ $a, $u, $v ] { $u %% $v } \

# compute b and c
==> map -> [ $a, $u, $v ] { my $b = $u div $v; [ $a, $b, $N - $a - $b ] } \

# compute product
==> map -> @triple { [*] @triple } \

# ... to give the result.
# XXX Rakudo feed operator wraps results in an extra sequence, thus .[0]
==> { .[0].say }();