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perf(sorted_set): O(n+m) co-iteration for set operations #3324

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perf(sorted_set): O(n+m) co-iteration for set operations #3324

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116 changes: 108 additions & 8 deletions sorted_set/set.mbt
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Original file line number Diff line number Diff line change
Expand Up @@ -262,7 +262,30 @@ pub fn[V : Compare] SortedSet::difference(
src : SortedSet[V],
) -> SortedSet[V] {
let ret = new()
self.each(x => if !src.contains(x) { ret.add(x) })
let it1 = self.iter()
let it2 = src.iter()
let mut a = it1.next()
let mut b = it2.next()
while a is Some(va) {
match b {
None => {
ret.add(va)
a = it1.next()
}
Some(vb) => {
let c = va.compare(vb)
if c < 0 {
ret.add(va)
a = it1.next()
} else if c > 0 {
b = it2.next()
} else {
a = it1.next()
b = it2.next()
}
}
}
}
ret
}

Expand Down Expand Up @@ -293,10 +316,38 @@ pub fn[V : Compare] SortedSet::symmetric_difference(
self : SortedSet[V],
other : SortedSet[V],
) -> SortedSet[V] {
// TODO: Optimize this function to avoid creating two intermediate sets.
let set1 = self.difference(other)
let set2 = other.difference(self)
set1.union(set2)
let ret = new()
let it1 = self.iter()
let it2 = other.iter()
let mut a = it1.next()
let mut b = it2.next()
while true {
match (a, b) {
(Some(va), Some(vb)) => {
let c = va.compare(vb)
if c < 0 {
ret.add(va)
a = it1.next()
} else if c > 0 {
ret.add(vb)
b = it2.next()
} else {
a = it1.next()
b = it2.next()
}
}
(Some(va), None) => {
ret.add(va)
a = it1.next()
}
(None, Some(vb)) => {
ret.add(vb)
b = it2.next()
}
(None, None) => break
}
}
ret
}

///|
Expand All @@ -307,7 +358,22 @@ pub fn[V : Compare] SortedSet::intersection(
src : SortedSet[V],
) -> SortedSet[V] {
let ret = new()
self.each(x => if src.contains(x) { ret.add(x) })
let it1 = self.iter()
let it2 = src.iter()
let mut a = it1.next()
let mut b = it2.next()
while a is Some(va) && b is Some(vb) {
let c = va.compare(vb)
if c < 0 {
a = it1.next()
} else if c > 0 {
b = it2.next()
} else {
ret.add(va)
a = it1.next()
b = it2.next()
}
}
ret
}

Expand All @@ -317,7 +383,27 @@ pub fn[V : Compare] SortedSet::subset(
self : SortedSet[V],
src : SortedSet[V],
) -> Bool {
self.iter().all(x => src.contains(x))
let it1 = self.iter()
let it2 = src.iter()
let mut a = it1.next()
let mut b = it2.next()
while a is Some(va) {
match b {
None => return false
Some(vb) => {
let c = va.compare(vb)
if c < 0 {
return false
} else if c > 0 {
b = it2.next()
} else {
a = it1.next()
b = it2.next()
}
}
}
}
true
}

///|
Expand All @@ -326,7 +412,21 @@ pub fn[V : Compare] SortedSet::disjoint(
self : SortedSet[V],
src : SortedSet[V],
) -> Bool {
self.iter().all(x => !src.contains(x))
let it1 = self.iter()
let it2 = src.iter()
let mut a = it1.next()
let mut b = it2.next()
while a is Some(va) && b is Some(vb) {
let c = va.compare(vb)
if c < 0 {
a = it1.next()
} else if c > 0 {
b = it2.next()
} else {
return false
}
}
true
}

// General collection operations
Expand Down
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