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merge: extract trivial_merge() that takes interleaved adds/removes iterator

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The Merge type will store interleaved terms instead of separate adds/removes
vecs.
This commit is contained in:
Yuya Nishihara 2023-11-03 11:11:39 +09:00
parent 01523ba4f3
commit 287728fee7
1 changed files with 23 additions and 15 deletions
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38
lib/src/merge.rs
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@ -43,17 +43,28 @@ where
removes.len() + 1,
"trivial_merge() requires exactly one more adds than removes"
);
trivial_merge_inner(
itertools::interleave(adds, removes),
adds.len() + removes.len(),
)
}
fn trivial_merge_inner<T>(mut values: impl Iterator<Item = T>, values_len: usize) -> Option<T>
where
T: Eq + Hash,
{
// Optimize the common cases of 3-way merge and 1-way (non-)merge
if adds.len() == 1 {
return Some(&adds[0]);
} else if adds.len() == 2 {
return if adds[0] == adds[1] {
Some(&adds[0])
} else if adds[0] == removes[0] {
Some(&adds[1])
} else if adds[1] == removes[0] {
Some(&adds[0])
if values_len == 1 {
let add = values.next().unwrap();
return Some(add);
} else if values_len == 3 {
let (add0, remove, add1) = values.next_tuple().unwrap();
return if add0 == add1 {
Some(add0)
} else if add0 == remove {
Some(add1)
} else if add1 == remove {
Some(add0)
} else {
None
};
@ -62,12 +73,9 @@ where
// Number of occurrences of each value, with positive indexes counted as +1 and
// negative as -1, thereby letting positive and negative terms with the same
// value (i.e. key in the map) cancel each other.
let mut counts: HashMap<&T, i32> = HashMap::new();
for value in adds.iter() {
counts.entry(value).and_modify(|e| *e += 1).or_insert(1);
}
for value in removes.iter() {
counts.entry(value).and_modify(|e| *e -= 1).or_insert(-1);
let mut counts: HashMap<T, i32> = HashMap::new();
for (value, n) in zip(values, [1, -1].into_iter().cycle()) {
counts.entry(value).and_modify(|e| *e += n).or_insert(n);
}
// Collect non-zero value. Values with a count of 0 means that they have