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Implemented iterator for partitions #3

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Implemented iterator for partitions #3

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144 changes: 72 additions & 72 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -31,68 +31,6 @@ impl Partitions {
}
}

/// Advances the iterator and returns the next partition.
#[inline]
pub fn next(&mut self) -> Option<&[usize]> {
let Partitions {
ref mut a,
ref mut k,
ref mut y,
ref mut next
} = *self;

match *next {
State::A => {
if *k == 0 {
if a.len() == 1 {
a.pop();
Some(&[])
} else {
None
}
} else {
*k -= 1;
let x = a[*k] + 1;

while 2 * x <= *y {
a[*k] = x;
*y -= x;
*k += 1;
}

let l = *k + 1;

if x <= *y {
a[*k] = x;
a[l] = *y;
*next = State::B { x, l };
Some(&a[..*k + 2])
} else {
a[*k] = x + *y;
*y = x + *y - 1;
Some(&a[..*k + 1])
}
}
},
State::B { mut x, l } => {
x += 1;
*y -= 1;

if x <= *y {
a[*k] = x;
a[l] = *y;
*next = State::B { x, l };
Some(&a[..*k + 2])
} else {
a[*k] = x + *y;
*y = x + *y - 1;
*next = State::A;
Some(&a[..*k + 1])
}
},
}
}

/// Makes a new iterator, trying to avoid allocations.
///
/// Any vector can be passed to this function, since its contents
Expand Down Expand Up @@ -126,26 +64,88 @@ impl Partitions {
}
}

impl Iterator for Partitions {
type Item = Vec<usize>;

fn next(&mut self) -> Option<Self::Item> {
let mut result = Vec::new();

match self.next {
State::A => {
if self.k == 0 {
if self.a.len() == 1 {
self.a.pop();
return Some(result);
} else {
return None;
}
} else {
self.k -= 1;
let x = self.a[self.k] + 1;

while 2 * x <= self.y {
self.a[self.k] = x;
self.y -= x;
self.k += 1;
}

let l = self.k + 1;

if x <= self.y {
self.a[self.k] = x;
self.a[l] = self.y;
self.next = State::B { x, l };
result.extend_from_slice(&self.a[..self.k + 2]);
} else {
self.a[self.k] = x + self.y;
self.y = x + self.y - 1;
result.extend_from_slice(&self.a[..self.k + 1]);
}
}
}
State::B { mut x, l } => {
x += 1;
self.y -= 1;

if x <= self.y {
self.a[self.k] = x;
self.a[l] = self.y;
self.next = State::B { x, l };
result.extend_from_slice(&self.a[..self.k + 2]);
} else {
self.a[self.k] = x + self.y;
self.y = x + self.y - 1;
self.next = State::A;
result.extend_from_slice(&self.a[..self.k + 1]);
}
}
}

Some(result)
}
}

#[test]
fn oeis() {
//! Tests the first few entries of A000041.

let tests: &[usize] = &[
1, 1, 2, 3, 5, 7, 11, 15, 22,
30, 42, 56, 77, 101, 135, 176, 231,
297, 385, 490, 627, 792, 1002, 1255, 1575,
1958, 2436, 3010, 3718, 4565, 5604, 6842, 8349,
10143, 12310, 14883, 17977, 21637, 26015, 31185, 37338,
44583, 53174, 63261, 75175, 89134, 105558, 124754, 147273,
173525,
1, 1, 2, 3, 5, 7, 11, 15, 22, 30, 42, 56, 77, 101, 135, 176, 231, 297, 385, 490, 627, 792,
1002, 1255, 1575, 1958, 2436, 3010, 3718, 4565, 5604, 6842, 8349, 10143, 12310, 14883,
17977, 21637, 26015, 31185, 37338, 44583, 53174, 63261, 75175, 89134, 105558, 124754,
147273, 173525,
];

for partition in Partitions::new(10) {
print!("{:?}\n", partition)
}

for (i, &n) in tests.iter().enumerate() {
let mut p = Partitions::new(i);
let p = Partitions::new(i);
let mut c = 0;

while let Some(x) = p.next() {
let sum: usize = x.iter().cloned().sum();
for partition in p {
let sum: usize = partition.iter().cloned().sum();
assert_eq!(sum, i);
c += 1;
}
Expand Down