dsalgo 0.2.6

A package for Datastructures and Algorithms.
Documentation 
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use crate::abstract_structs;

/// explicit lifetime for Monoid<S>.
/// S implements Copy trait for convenience.
pub struct SegmentTree<'a, S: Copy> {
    monoid: abstract_structs::Monoid<'a, S>,
    data: Vec<S>,
    size: usize,
}

impl<'a, S: std::fmt::Debug + Copy> std::fmt::Debug for SegmentTree<'a, S> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_tuple("SegmentTree").field(&self.data).finish()
    }
}

impl<'a, S: Copy> SegmentTree<'a, S> {
    pub fn new(monoid: abstract_structs::Monoid<'a, S>, n: usize) -> Self {
        let arr = vec![(monoid.identity)(); n];
        Self::from_vec(monoid, &arr)
    }

    pub fn from_vec(
        monoid: abstract_structs::Monoid<'a, S>,
        a: &Vec<S>,
    ) -> Self {
        let size = a.len();
        let n = size.next_power_of_two();
        let mut data = vec![(monoid.identity)(); n << 1];
        for i in 0..size {
            data[n + i] = a[i];
        }
        let mut seg = Self {
            monoid,
            data,
            size,
        };
        for i in (0..n).rev() {
            seg.merge(i);
        }
        seg
    }

    fn merge(&mut self, i: usize) {
        self.data[i] =
            (self.monoid.operate)(&self.data[i << 1], &self.data[i << 1 | 1]);
    }

    pub fn set(&mut self, mut i: usize, x: S) {
        assert!(i < self.size);
        i += self.data.len() >> 1;
        self.data[i] = x;
        while i > 1 {
            i >>= 1;
            self.merge(i);
        }
    }

    pub fn get(&self, mut l: usize, mut r: usize) -> S {
        assert!(l <= r && r <= self.size);
        let n = self.data.len() >> 1;
        l += n;
        r += n;
        let mut vl = (self.monoid.identity)();
        let mut vr = (self.monoid.identity)();
        while l < r {
            if l & 1 == 1 {
                vl = (self.monoid.operate)(&vl, &self.data[l]);
                l += 1;
            }
            if r & 1 == 1 {
                r -= 1;
                vr = (self.monoid.operate)(&self.data[r], &vr);
            }
            l >>= 1;
            r >>= 1;
        }
        (self.monoid.operate)(&vl, &vr)
    }

    pub fn max_right(
        &self,
        is_ok: Box<dyn Fn(&S) -> bool>,
        l: usize,
    ) -> usize {
        assert!(l < self.size);
        let n = self.data.len() >> 1;
        let mut v = (self.monoid.identity)();
        let mut i = (l + n) as i32;
        loop {
            i /= i & -i;
            if is_ok(&(self.monoid.operate)(&v, &self.data[i as usize])) {
                v = (self.monoid.operate)(&v, &self.data[i as usize]);
                i += 1;
                if i & -i == i {
                    return self.size;
                }
                continue;
            }
            while i < n as i32 {
                i <<= 1;
                if is_ok(&(self.monoid.operate)(&v, &self.data[i as usize])) {
                    v = (self.monoid.operate)(&v, &self.data[i as usize]);
                }
            }
            return i as usize - n;
        }
    }
}

impl<'a, S: Copy> std::ops::Index<usize> for SegmentTree<'a, S> {
    type Output = S;

    fn index(&self, i: usize) -> &Self::Output {
        assert!(i < self.size);
        &self.data[i + (self.data.len() >> 1)]
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_segment_tree() {
        let op = |x: &i32, y: &i32| x + y;
        let e = || 0;
        let m = abstract_structs::Monoid::<i32> {
            operate: &op,
            identity: &e,
            commutative: true,
            idempotent: false,
        };
        let mut a = vec![0i32; 10];
        for i in 0..10i32 {
            a[i as usize] = i;
        }
        let mut seg = SegmentTree::from_vec(m, &a);
        assert_eq!(seg.get(0, 10), 45);
        assert_eq!(
            seg.data,
            [
                45, 45, 28, 17, 6, 22, 17, 0, 1, 5, 9, 13, 17, 0, 0, 0, 0, 1,
                2, 3, 4, 5, 6, 7, 8, 9, 0, 0, 0, 0, 0, 0
            ],
        );
        println!("{:?}", seg);
        seg.set(4, 8);
        assert_eq!(seg.get(3, 8), 29);
    }
}