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* array.c (rb_ary_combination): Support for Array#combination.size

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[Feature #6636]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37502 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
This commit is contained in:
marcandre 2012-11-06 17:11:21 +00:00
parent 1cb9f27c13
commit 6bbf668d6e
2 changed files with 32 additions and 2 deletions
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29
array.c
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@ -26,7 +26,7 @@
VALUE rb_cArray; VALUE rb_cArray;
static ID id_cmp; static ID id_cmp, id_div;
#define ARY_DEFAULT_SIZE 16 #define ARY_DEFAULT_SIZE 16
#define ARY_MAX_SIZE (LONG_MAX / (int)sizeof(VALUE)) #define ARY_MAX_SIZE (LONG_MAX / (int)sizeof(VALUE))
@ -1539,6 +1539,9 @@ rb_ary_insert(int argc, VALUE *argv, VALUE ary)
return ary; return ary;
} }
static VALUE
rb_ary_length(VALUE ary);
/* /*
* call-seq: * call-seq:
* ary.each { |item| block } -> ary * ary.each { |item| block } -> ary
@ -4337,6 +4340,18 @@ descending_factorial(long from, long how_many)
return cnt; return cnt;
} }
static VALUE
binomial_coefficient(long comb, long size)
{
if (comb > size-comb) {
comb = size-comb;
}
if (comb < 0) {
return LONG2FIX(0);
}
return rb_funcall(descending_factorial(size, comb), id_div, 1, descending_factorial(comb, comb));
}
static VALUE static VALUE
rb_ary_permutation_size(VALUE ary, VALUE args) rb_ary_permutation_size(VALUE ary, VALUE args)
{ {
@ -4414,6 +4429,15 @@ rb_ary_permutation(int argc, VALUE *argv, VALUE ary)
return ary; return ary;
} }
static VALUE
rb_ary_combination_size(VALUE ary, VALUE args)
{
long n = RARRAY_LEN(ary);
long k = NUM2LONG(RARRAY_PTR(args)[0]);
return binomial_coefficient(k, n);
}
/* /*
* call-seq: * call-seq:
* ary.combination(n) { |c| block } -> ary * ary.combination(n) { |c| block } -> ary
@ -4445,7 +4469,7 @@ rb_ary_combination(VALUE ary, VALUE num)
long n, i, len; long n, i, len;
n = NUM2LONG(num); n = NUM2LONG(num);
RETURN_ENUMERATOR(ary, 1, &num); RETURN_SIZED_ENUMERATOR(ary, 1, &num, rb_ary_combination_size);
len = RARRAY_LEN(ary); len = RARRAY_LEN(ary);
if (n < 0 || len < n) { if (n < 0 || len < n) {
/* yield nothing */ /* yield nothing */
@ -5237,4 +5261,5 @@ Init_Array(void)
id_cmp = rb_intern("<=>"); id_cmp = rb_intern("<=>");
sym_random = ID2SYM(rb_intern("random")); sym_random = ID2SYM(rb_intern("random"));
id_div = rb_intern("div");
} }

5
test/ruby/test_enumerator.rb
View File

@ -441,6 +441,11 @@ class TestEnumerator < Test::Unit::TestCase
assert_equal 24, [0, 1, 2, 4].permutation.size assert_equal 24, [0, 1, 2, 4].permutation.size
assert_equal 2933197128679486453788761052665610240000000, assert_equal 2933197128679486453788761052665610240000000,
(1..42).to_a.permutation(30).size # 1.upto(42).inject(:*) / 1.upto(12).inject(:*) (1..42).to_a.permutation(30).size # 1.upto(42).inject(:*) / 1.upto(12).inject(:*)
check_consistency_for_combinatorics(:combination)
assert_equal 28258808871162574166368460400,
(1..100).to_a.combination(42).size
# 1.upto(100).inject(:*) / 1.upto(42).inject(:*) / 1.upto(58).inject(:*)
end end
end end