master > master: code-rust - tarjan alg
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code/rust/src/graphs/tarjan.rs
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176
code/rust/src/graphs/tarjan.rs
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// ----------------------------------------------------------------
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// IMPORTS
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// ----------------------------------------------------------------
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use std::fmt::Display;
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use std::hash::Hash;
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use std::collections::HashMap;
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use crate::core::utils;
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use crate::stacks::stack::Stack;
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use crate::graphs::graph::Graph;
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// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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// CONSTANTS
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// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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#[derive(Clone, Copy, PartialEq)]
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enum State {
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UNTOUCHED,
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PENDING,
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FINISHED,
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}
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// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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// METHOD Tarjan Algorithm
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// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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/// # Tarjan Algorithm #
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/// Runs the Tarjan-Algorithm to compute the strongly connected components.
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pub fn tarjan_algorithm<T>(gph: &Graph<T>) -> Vec<Vec<T>>
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where T: Eq + Hash + Clone + Display
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{
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let mut ctx = Context::new(&gph);
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for u in gph.nodes.iter() {
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tarjan_visit(gph, u, &mut ctx);
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}
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return ctx.components;
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}
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/// recursive depth-first search algorithm to compute components
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fn tarjan_visit<T>(gph: &Graph<T>, v: &T, ctx: &mut Context<T>)
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where T: Eq + Hash + Clone + Display
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{
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if !(ctx.get_state(v) == State::UNTOUCHED) {
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return;
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}
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ctx.max_index += 1;
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ctx.push(v);
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ctx.set_root(v, ctx.max_index);
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ctx.set_index(v, ctx.max_index);
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ctx.set_state(v, State::PENDING);
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// depth first search:
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for u in gph.successors(&v) {
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tarjan_visit(gph, &u, ctx);
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// remains relevant for v, provided u still in Stack:
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if ctx.stack.elements.contains(&u) {
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let root = utils::min(
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ctx.get_root(&u),
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ctx.get_root(v)
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);
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ctx.set_root(v, root);
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}
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}
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ctx.set_state(v, State::FINISHED);
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if ctx.get_index(v) == ctx.get_root(v) {
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let mut component: Vec<T> = Vec::new();
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loop {
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let u = ctx.top();
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ctx.pop();
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component.push(u.clone());
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if u == *v {
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break;
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}
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}
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ctx.components.push(component);
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}
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}
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// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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// AUXILIARY context variables for algorithm
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// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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#[derive(Clone, Copy)]
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struct NodeInformation {
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root: usize,
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index: usize,
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state: State,
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}
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struct Context<T> {
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stack: Stack<T>,
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max_index: usize,
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infos: HashMap<T, NodeInformation>,
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components: Vec<Vec<T>>,
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}
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impl<T> Context<T>
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where T: Eq + Hash + Clone + Display
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{
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fn new(gph: &Graph<T>) -> Context<T> {
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let mut infos = HashMap::<T, NodeInformation>::new();
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for u in gph.nodes.iter() {
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infos.entry(u.clone()).or_insert(NodeInformation::new());
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}
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return Context {
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stack: Stack::new(),
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max_index: 0,
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infos: infos,
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components: vec![],
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};
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}
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fn push(self: &mut Self, u: &T) {
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self.stack.push(u.clone());
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}
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fn top(self: &mut Self) -> T {
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return self.stack.top();
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}
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fn pop(self: &mut Self) -> T {
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return self.stack.pop();
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}
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fn update_infos(self: &mut Self, u: &T, info: NodeInformation) {
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self.infos.insert(u.clone(), info);
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}
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fn set_state(self: &mut Self, u: &T, state: State) {
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let mut info = *self.infos.get(u).unwrap();
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info.state = state;
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self.update_infos(u, info);
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}
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fn set_root(self: &mut Self, u: &T, root: usize) {
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let mut info = *self.infos.get(u).unwrap();
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info.root = root;
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self.update_infos(u, info);
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}
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fn set_index(self: &mut Self, u: &T, index: usize) {
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let mut info = *self.infos.get(u).unwrap();
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info.index = index;
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self.update_infos(u, info);
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}
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fn get_state(self: &mut Self, u: &T) -> State {
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let info = *self.infos.get(u).unwrap();
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return info.state;
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}
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fn get_root(self: &mut Self, u: &T) -> usize {
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let info = *self.infos.get(u).unwrap();
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return info.root;
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}
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fn get_index(self: &mut Self, u: &T) -> usize {
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let info = *self.infos.get(u).unwrap();
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return info.index;
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}
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}
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impl NodeInformation {
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fn new() -> NodeInformation {
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return NodeInformation {
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root: 0,
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index: 0,
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state: State::UNTOUCHED,
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};
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}
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}
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