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Permutations unnecessarily complex 1 #748

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merged 2 commits into from
Sep 6, 2023
Merged

Permutations unnecessarily complex 1 #748

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2618cd3
Simplify Permutations (1.1) move impl Permutations
phimuemue Sep 6, 2023
21608b5
Simplify Permutations (1.2) inline Permutations::advance
phimuemue Sep 6, 2023
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67 changes: 27 additions & 40 deletions src/permutations.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -91,10 +91,35 @@ where
type Item = Vec<I::Item>;

fn next(&mut self) -> Option<Self::Item> {
self.advance();
{
let &mut Permutations { ref mut vals, ref mut state } = self;
match *state {
PermutationState::StartUnknownLen { k } => {
*state = PermutationState::OngoingUnknownLen { k, min_n: k };
},
PermutationState::OngoingUnknownLen { k, min_n } => {
if vals.get_next() {
*state = PermutationState::OngoingUnknownLen { k, min_n: min_n + 1 };
} else {
let n = min_n;
let prev_iteration_count = n - k + 1;
let mut complete_state = CompleteState::Start { n, k };

let &mut Permutations { ref vals, ref state } = self;
// Advance the complete-state iterator to the correct point
for _ in 0..(prev_iteration_count + 1) {
complete_state.advance();
}

*state = PermutationState::Complete(complete_state);
}
},
PermutationState::Complete(ref mut state) => {
state.advance();
},
PermutationState::Empty => {},
};
}
let &mut Permutations { ref vals, ref state } = self;
match *state {
PermutationState::StartUnknownLen { .. } => panic!("unexpected iterator state"),
PermutationState::OngoingUnknownLen { k, min_n } => {
Expand Down Expand Up @@ -159,44 +184,6 @@ where
}
}

impl<I> Permutations<I>
where
I: Iterator,
I::Item: Clone
{
fn advance(&mut self) {
let &mut Permutations { ref mut vals, ref mut state } = self;

*state = match *state {
PermutationState::StartUnknownLen { k } => {
PermutationState::OngoingUnknownLen { k, min_n: k }
}
PermutationState::OngoingUnknownLen { k, min_n } => {
if vals.get_next() {
PermutationState::OngoingUnknownLen { k, min_n: min_n + 1 }
} else {
let n = min_n;
let prev_iteration_count = n - k + 1;
let mut complete_state = CompleteState::Start { n, k };

// Advance the complete-state iterator to the correct point
for _ in 0..(prev_iteration_count + 1) {
complete_state.advance();
}

PermutationState::Complete(complete_state)
}
}
PermutationState::Complete(ref mut state) => {
state.advance();

return;
}
PermutationState::Empty => { return; }
};
}
}

impl CompleteState {
fn advance(&mut self) {
*self = match *self {
Expand Down