src/disjoint_set.rs

/// Very simple disjoint set implementation for clustering cropped textures
/// - fixed size
/// - cannot divide the union
pub struct DisjointSet {
    parent: Vec<usize>,
}

impl DisjointSet {
    pub fn new(num_elements: usize) -> Self {
        DisjointSet {
            parent: (0..num_elements).collect(),
        }
    }

    #[inline]
    pub fn root(&self, x: usize) -> usize {
        if self.parent[x] == x {
            x
        } else {
            self.root(self.parent[x])
        }
    }

    #[inline]
    pub fn unite(&mut self, x: usize, y: usize) {
        let root_x = self.root(x);
        let root_y = self.root(y);
        self.parent[root_x] = root_y;
    }

    #[allow(dead_code)]
    fn is_same(&self, x: usize, y: usize) -> bool {
        self.root(x) == self.root(y)
    }

    #[inline]
    pub fn compress(&mut self) {
        self.parent = self.parent.iter().map(|&x| self.root(x)).collect();
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_disjoint_set_unite() {
        let mut ds = DisjointSet::new(5);
        ds.unite(0, 1);
        ds.unite(3, 4);
        ds.unite(1, 2);
        assert!(ds.is_same(0, 2));
        assert!(!ds.is_same(0, 3));

        ds.unite(0, 3);
        assert!(ds.is_same(0, 4));
    }
}