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Fix FromIterator for Segtree #138

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Merged
merged 2 commits into from
Feb 24, 2025
Merged

Fix FromIterator for Segtree #138

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05e2c00
fix FromIterator for Segtree
mousecrusher2 Feb 13, 2024
23ccb58
remove unnecessary vec!
mousecrusher2 Feb 14, 2024
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30 changes: 14 additions & 16 deletions src/segtree.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -137,22 +137,8 @@ impl<M: Monoid> From<Vec<M::S>> for Segtree<M> {
}
impl<M: Monoid> FromIterator<M::S> for Segtree<M> {
fn from_iter<T: IntoIterator<Item = M::S>>(iter: T) -> Self {
let iter = iter.into_iter();
let n = iter.size_hint().0;
let log = ceil_pow2(n as u32) as usize;
let size = 1 << log;
let mut d = Vec::with_capacity(size * 2);
d.extend(
std::iter::repeat_with(M::identity)
.take(size)
.chain(iter)
.chain(std::iter::repeat_with(M::identity).take(size - n)),
);
let mut ret = Segtree { n, size, log, d };
for i in (1..size).rev() {
ret.update(i);
}
ret
let v = iter.into_iter().collect::<Vec<_>>();
v.into()
}
}
impl<M: Monoid> Segtree<M> {
Expand Down Expand Up @@ -353,6 +339,18 @@ mod tests {
check_segtree(&internal, &segtree);
}

#[test]
fn test_segtree_fromiter() {
let v = [1, 4, 1, 4, 2, 1, 3, 5, 6];
let base = v
.iter()
.copied()
.filter(|&x| x % 2 == 0)
.collect::<Vec<_>>();
let segtree: Segtree<Max<_>> = v.iter().copied().filter(|&x| x % 2 == 0).collect();
check_segtree(&base, &segtree);
}

//noinspection DuplicatedCode
fn check_segtree(base: &[i32], segtree: &Segtree<Max<i32>>) {
let n = base.len();
Expand Down