1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128

use std::collections::VecDeque;

const MAX_PARENT: usize = 1 << 50;
pub struct LowestCommonAncestor {
    parent: Vec<Vec<usize>>,
    depth: Vec<usize>,
    log_v: usize,
}

impl LowestCommonAncestor {
    pub fn new(graph: &Vec<Vec<usize>>) -> Self {
        let num_v = graph.len();
        let root = 0;
        let mut depth = vec![0; num_v];

        let mut log_v = 1;
        let mut i = 1;
        while i <= num_v {
            i *= 2;
            log_v += 1;
        }
        let mut parent: Vec<Vec<usize>> = vec![vec![0; num_v]; log_v];

        let mut depth_vis = vec![false; num_v];
        let mut stack = VecDeque::new();
        stack.push_front(root);
        parent[0][root] = MAX_PARENT;
        depth[root] = 0;
        depth_vis[root] = true;
        while !stack.is_empty() {
            let v = stack.pop_front().unwrap();
            stack.push_front(v);
            for &u in &graph[v] {
                if depth_vis[u] {
                    continue;
                }
                parent[0][u] = v;
                depth[u] = depth[v] + 1;
                depth_vis[u] = true;
                stack.push_front(u);
            }

            let head = stack.pop_front().unwrap();
            if head != v {
                stack.push_front(head);
            }
        }

        for k in 0..(log_v - 1) {
            for u in 0..num_v {
                parent[k + 1][u] = if parent[k][u] == MAX_PARENT {
                    MAX_PARENT
                } else {
                    parent[k][parent[k][u]]
                };
            }
        }

        LowestCommonAncestor {
            parent: parent,
            depth: depth,
            log_v: log_v,
        }
    }

    pub fn get_lca(&self, u: usize, v: usize) -> usize {
        let (mut u, mut v) = if self.depth[u] <= self.depth[v] {
            (u, v)
        } else {
            (v, u)
        };
        for k in 0..self.log_v {
            if ((self.depth[v] - self.depth[u]) & (1 << k)) != 0 {
                v = self.parent[k][v];
            }
        }
        if u == v {
            return u;
        }

        for k in (0..self.log_v).rev() {
            if self.parent[k][u] != self.parent[k][v] {
                u = self.parent[k][u];
                v = self.parent[k][v];
            }
        }
        return self.parent[0][u];
    }

    pub fn get_dist(&self, u: usize, v: usize) -> usize {
        let lca = self.get_lca(u, v);
        self.depth[u] + self.depth[v] - self.depth[lca] * 2
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::utils::test_helper;
    use crate::utils::test_helper::Tester;

    #[test]
    fn solve_grl_5_c() {
        let tester = Tester::new("./assets/GRL_5_C/in/", "./assets/GRL_5_C/out/");
        tester.test_solution(|sc| {
            let n: usize = sc.read();
            let mut graph = (0..n).map(|_| Vec::new()).collect::<Vec<_>>();
            for i in 0..n {
                let k = sc.read();
                for _ in 0..k {
                    let c: usize = sc.read();
                    graph[i].push(c);
                    graph[c].push(i);
                }
            }

            let lca = LowestCommonAncestor::new(&graph);

            let q: usize = sc.read();
            for _ in 0..q {
                let u: usize = sc.read();
                let v: usize = sc.read();
                let ans = lca.get_lca(u, v);
                sc.write(format!("{}\n", ans));
            }
        });
    }
}