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use crate::graph::def::Graph;
use std::cmp::Reverse;
use std::collections::{BinaryHeap, HashMap};
use cargo_snippet::snippet;
#[snippet("dijkstra")]
pub struct Dijkstra {
g: Vec<Vec<usize>>,
e: HashMap<(usize, usize), u64>,
}
#[snippet("dijkstra")]
impl<'a> Graph<'a> for Dijkstra {
type NodeId = usize;
type Iter = std::iter::Cloned<std::slice::Iter<'a, Self::NodeId>>;
fn len(&self) -> usize {
self.g.len()
}
fn is_empty(&self) -> bool {
self.len() == 0
}
fn index(&self, a: Self::NodeId) -> usize {
a
}
fn neighbors(&'a self, a: Self::NodeId) -> Self::Iter {
self.g[a].iter().cloned()
}
}
#[snippet("dijkstra")]
pub fn make_graph_for_dijkstra(n: usize, edges: &[(usize, usize, u64)]) -> Dijkstra {
let mut g = vec![Vec::new(); n];
let mut e = HashMap::new();
for (from, to, weight) in edges.iter() {
g[*from].push(*to);
g[*to].push(*from);
e.insert((*from, *to), *weight);
e.insert((*to, *from), *weight);
}
Dijkstra { g, e }
}
#[snippet("dijkstra")]
impl<'a> Dijkstra {
pub fn weight(&self, from: usize, to: usize) -> u64 {
self.e[&(from, to)]
}
pub fn add_edge(&mut self, edge: (usize, usize, u64)) {
self.g[edge.0].push(edge.1);
self.g[edge.1].push(edge.0);
self.e.insert((edge.0, edge.1), edge.2);
self.e.insert((edge.1, edge.0), edge.2);
}
}
#[snippet("dijkstra")]
pub fn dijkstra<'a>(g: &'a Dijkstra, start: usize) -> Vec<u64> {
let mut d = Vec::with_capacity(g.len());
let mut q: BinaryHeap<Reverse<(u64, usize)>> = BinaryHeap::with_capacity(g.len());
for i in 0..g.len() {
let j = if i == start { 0 } else { std::u64::MAX };
d.push(j);
q.push(Reverse((j, i)));
}
while !q.is_empty() {
let u = q.pop().unwrap().0;
for v in g.neighbors(u.1) {
let w = g.weight(u.1, v);
if d[v] > d[u.1] + w {
d[v] = d[u.1] + w;
q.push(Reverse((w, v)));
}
}
}
d
}
#[snippet("dijkstra")]
pub fn dijkstra_with_path<'a>(g: &'a Dijkstra, start: usize, goal: usize) -> (Vec<usize>, u64) {
let mut d = Vec::with_capacity(g.len());
let mut q: BinaryHeap<Reverse<(u64, usize)>> = BinaryHeap::with_capacity(g.len());
for i in 0..g.len() {
let j = if i == start { 0 } else { std::u64::MAX };
d.push(j);
q.push(Reverse((j, i)));
}
let mut p: Vec<Option<usize>> = vec![None; g.len()];
while !q.is_empty() {
let u = q.pop().unwrap().0;
for v in g.neighbors(u.1) {
let w = g.weight(u.1, v);
if d[v] > d[u.1] + w {
d[v] = d[u.1] + w;
p[v] = Some(u.1);
q.push(Reverse((w, v)));
}
}
}
let mut path = vec![goal];
loop {
match p[*path.last().unwrap()] {
Some(prev) if prev == start => {
path.push(prev);
break;
}
Some(prev) => {
path.push(prev);
}
None => break,
}
}
path.reverse();
(path, d[goal])
}
#[test]
fn dijkstra_test() {
let mut d = make_graph_for_dijkstra(4, &[(0, 1, 2), (0, 2, 100), (1, 3, 10), (2, 3, 100)]);
assert_eq!(dijkstra(&d, 0)[3], 12);
d.add_edge((0, 3, 1));
assert_eq!(dijkstra(&d, 0)[2], 100);
let p = dijkstra_with_path(&d, 0, 3).0;
assert_eq!(p, vec![0, 3]);
}