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IterBinomial: Only return coefficient

This commit is contained in:
Vinzent Steinberg 2017-03-20 10:20:15 +01:00
parent e486e6a981
commit 47613ff5ff
1 changed files with 8 additions and 9 deletions
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17
integer/src/lib.rs
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@ -675,7 +675,7 @@ pub struct IterBinomial<T> {
impl<T> IterBinomial<T> impl<T> IterBinomial<T>
where T: Integer, where T: Integer,
{ {
/// For a given n, iterate over all binomial coefficients ((k, n - k), binomial(n, k)). /// For a given n, iterate over all binomial coefficients binomial(n, k), for k=0...n.
pub fn new(n: T) -> IterBinomial<T> { pub fn new(n: T) -> IterBinomial<T> {
IterBinomial { IterBinomial {
k: T::zero(), a: T::one(), n: n k: T::zero(), a: T::one(), n: n
@ -686,9 +686,9 @@ impl<T> IterBinomial<T>
impl<T> Iterator for IterBinomial<T> impl<T> Iterator for IterBinomial<T>
where T: Integer + Clone where T: Integer + Clone
{ {
type Item = ((T, T), T); type Item = T;
fn next(&mut self) -> Option<((T, T), T)> { fn next(&mut self) -> Option<T> {
if self.k > self.n { if self.k > self.n {
return None; return None;
} }
@ -697,11 +697,8 @@ impl<T> Iterator for IterBinomial<T>
} else { } else {
T::one() T::one()
}; };
let r = Some(
((self.k.clone(), self.n.clone() - self.k.clone()),
self.a.clone()));
self.k = self.k.clone() + T::one(); self.k = self.k.clone() + T::one();
r Some(self.a.clone())
} }
} }
@ -768,7 +765,7 @@ fn test_binomial_coeff() {
($t:ty) => { { ($t:ty) => { {
let n: $t = 3; let n: $t = 3;
let c: Vec<_> = IterBinomial::new(n).collect(); let c: Vec<_> = IterBinomial::new(n).collect();
let expected = vec![((0, 3), 1), ((1, 2), 3), ((2, 1), 3), ((3, 0), 1)]; let expected = vec![1, 3, 3, 1];
assert_eq!(c, expected); assert_eq!(c, expected);
} } } }
} }
@ -786,8 +783,10 @@ fn test_binomial_coeff() {
($t:ty, $n:expr) => { { ($t:ty, $n:expr) => { {
let n: $t = $n; let n: $t = $n;
let c: Vec<_> = IterBinomial::new(n).collect(); let c: Vec<_> = IterBinomial::new(n).collect();
for &((k, _), b) in &c { let mut k: $t = 0;
for b in c {
assert_eq!(b, binomial(n, k)); assert_eq!(b, binomial(n, k));
k += 1;
} }
} } } }
} }