day23: problem 2 solution
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228
23/src/main.rs
228
23/src/main.rs
@ -2,7 +2,7 @@ use itertools::Itertools;
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use ndarray::prelude::*;
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use petgraph::algo::all_simple_paths;
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use petgraph::prelude::*;
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use std::collections::HashMap;
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use std::collections::{HashMap, HashSet};
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use std::fmt::{Debug, Display, Write};
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use std::fs::File;
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use std::io::{BufRead, BufReader, Lines};
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@ -31,25 +31,31 @@ fn main() {
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// PARSE
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#[derive(Debug, Clone)]
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enum EdgeType {
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FromPath,
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FromSlope,
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}
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#[derive(Debug, Clone)]
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#[derive(Clone)]
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struct Node {
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c: char,
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pos: Position,
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}
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impl Display for Node {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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write!(f, "({},{})", self.pos.0, self.pos.1)
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}
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}
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impl Debug for Node {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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write!(f, "({},{})", self.pos.0, self.pos.1)
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}
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}
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type Position = (usize, usize);
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#[derive(Clone)]
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struct ForestMap {
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map: Array2<char>,
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indexes: HashMap<Position, NodeIndex>,
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graph: DiGraph<Node, EdgeType>,
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graph: StableDiGraph<Node, u64>,
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start: Position,
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end: Position,
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}
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@ -91,7 +97,7 @@ impl<T: BufRead> From<Lines<T>> for ForestMap {
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map.len_of(Axis(1)) - 1,
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);
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let mut graph = Graph::default();
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let mut graph = StableGraph::default();
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let mut indexes = HashMap::new();
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for (pos, c) in map.indexed_iter() {
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if *c != '#' {
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@ -99,47 +105,6 @@ impl<T: BufRead> From<Lines<T>> for ForestMap {
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}
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}
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for (pos, c) in map.indexed_iter() {
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match c {
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'#' => continue,
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'.' => {
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adjacent_to(&map, pos).iter().for_each(|adj| {
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if indexes.contains_key(&adj) {
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graph.add_edge(indexes[&pos], indexes[adj], EdgeType::FromPath);
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}
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});
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}
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'^' => {
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if let Some(adj) = offset_pos(&map, pos, (0, -1)) {
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if indexes.contains_key(&adj) {
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graph.add_edge(indexes[&pos], indexes[&adj], EdgeType::FromSlope);
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}
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}
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}
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'>' => {
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if let Some(adj) = offset_pos(&map, pos, (1, 0)) {
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if indexes.contains_key(&adj) {
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graph.add_edge(indexes[&pos], indexes[&adj], EdgeType::FromSlope);
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}
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}
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}
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'v' => {
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if let Some(adj) = offset_pos(&map, pos, (0, 1)) {
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if indexes.contains_key(&adj) {
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graph.add_edge(indexes[&pos], indexes[&adj], EdgeType::FromSlope);
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}
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}
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}
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'<' => {
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if let Some(adj) = offset_pos(&map, pos, (-1, 0)) {
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if indexes.contains_key(&adj) {
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graph.add_edge(indexes[&pos], indexes[&adj], EdgeType::FromSlope);
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}
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}
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}
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c => panic!("invalid map character {}", c),
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}
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}
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Self {
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map,
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start,
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@ -150,6 +115,129 @@ impl<T: BufRead> From<Lines<T>> for ForestMap {
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}
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}
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impl ForestMap {
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fn build_graph(&mut self) {
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for (pos, c) in self.map.indexed_iter() {
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match c {
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'#' => continue,
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'.' => {
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adjacent_to(&self.map, pos).iter().for_each(|adj| {
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if self.indexes.contains_key(&adj) {
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self.graph.add_edge(self.indexes[&pos], self.indexes[adj], 1);
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}
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});
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}
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'^' => {
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if let Some(adj) = offset_pos(&self.map, pos, (0, -1)) {
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if self.indexes.contains_key(&adj) {
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self.graph.add_edge(self.indexes[&pos], self.indexes[&adj], 1);
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}
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}
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}
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'>' => {
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if let Some(adj) = offset_pos(&self.map, pos, (1, 0)) {
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if self.indexes.contains_key(&adj) {
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self.graph.add_edge(self.indexes[&pos], self.indexes[&adj], 1);
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}
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}
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}
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'v' => {
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if let Some(adj) = offset_pos(&self.map, pos, (0, 1)) {
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if self.indexes.contains_key(&adj) {
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self.graph.add_edge(self.indexes[&pos], self.indexes[&adj], 1);
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}
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}
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}
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'<' => {
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if let Some(adj) = offset_pos(&self.map, pos, (-1, 0)) {
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if self.indexes.contains_key(&adj) {
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self.graph.add_edge(self.indexes[&pos], self.indexes[&adj], 1);
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}
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}
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}
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c => panic!("invalid map character {}", c),
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}
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}
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}
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fn build_graph2(&mut self) {
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for (pos, c) in self.map.indexed_iter() {
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match c {
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'#' => continue,
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'.' | '^' | '>' | 'v' | '<' => {
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adjacent_to(&self.map, pos).iter().for_each(|adj| {
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if self.indexes.contains_key(&adj) {
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self.graph.add_edge(self.indexes[&pos], self.indexes[adj], 1);
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}
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});
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}
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c => panic!("invalid map character {}", c),
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}
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}
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}
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// Cull nodes that don't change the topology of the graph and combine their cost
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fn simplify_graph(&mut self) {
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let mut idxs: Vec<_> = self
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.graph
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.neighbors(self.indexes[&self.start])
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.map(|idx| (self.indexes[&self.start], idx))
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.collect();
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let mut visited = HashSet::from([self.indexes[&self.start]]);
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while let Some((last_idx, cur_idx)) = idxs.pop() {
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if !visited.insert(cur_idx) {
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continue;
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}
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let our_neighbors = self.graph.neighbors(cur_idx).collect_vec();
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// if we have exactly 2 neighbours, then one is where we came from, and we can shortcut this node with a
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// pair of new edges A <-> C and break the existing 4 edges between them
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if our_neighbors.len() == 2 {
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let next_idx = our_neighbors.iter().find(|n| **n != last_idx).unwrap();
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// remove the 4 existing edges
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// careful of order of operations, as removing edges invalidates edge indexes
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let forward_cost = self
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.graph
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.remove_edge(self.graph.find_edge(cur_idx, *next_idx).unwrap())
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.unwrap();
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let last_forward_cost = self
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.graph
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.remove_edge(self.graph.find_edge(last_idx, cur_idx).unwrap())
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.unwrap();
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let backward_cost = self
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.graph
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.remove_edge(self.graph.find_edge(cur_idx, last_idx).unwrap())
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.unwrap();
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let next_backward_cost = self
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.graph
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.remove_edge(self.graph.find_edge(*next_idx, cur_idx).unwrap())
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.unwrap();
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let new_forward_cost = forward_cost + last_forward_cost;
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let new_backward_cost = backward_cost + next_backward_cost;
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// add edge from last to next
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self.graph.add_edge(last_idx, *next_idx, new_forward_cost);
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self.graph.add_edge(*next_idx, last_idx, new_backward_cost);
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self.graph.remove_node(cur_idx);
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// push the next node
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idxs.push((last_idx, *next_idx));
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} else {
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// don't do anything about nodes with > 2 edges, just push them onto the stack, if there are some
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idxs.append(
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&mut self
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.graph
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.neighbors(cur_idx)
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.into_iter()
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.map(|next_idx| (cur_idx, next_idx))
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.collect(),
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);
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}
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}
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}
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}
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impl Debug for ForestMap {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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for y in 0..self.map.len_of(Axis(1)) {
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@ -158,20 +246,6 @@ impl Debug for ForestMap {
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}
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writeln!(f)?;
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}
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// println!("start: {:?} end: {:?}", self.start, self.end);
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// println!("digraph aoc23 {{");
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// for node in self.graph.node_indices() {
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// println!(
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// " \"{},{}\" -> {}",
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// self.graph[node].pos.0,
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// self.graph[node].pos.1,
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// self.graph
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// .neighbors(node)
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// .map(|n| format!("\"{},{}\"", self.graph[n].pos.0, self.graph[n].pos.1))
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// .join(",")
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// );
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// }
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// println!("}}");
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Ok(())
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}
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}
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@ -179,8 +253,9 @@ impl Debug for ForestMap {
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// PROBLEM 1 solution
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fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
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let map = ForestMap::from(input);
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println!("{:?}", map);
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let mut map = ForestMap::from(input);
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map.build_graph();
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// println!("{:?}", map);
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let paths = all_simple_paths::<Vec<_>, _>(&map.graph, map.indexes[&map.start], map.indexes[&map.end], 0, None)
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.collect_vec();
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let longest = paths.iter().max_by_key(|path| path.len()).unwrap();
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@ -188,9 +263,24 @@ fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
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longest.len() as u64 - 1
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}
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fn calc_path_length(map: &ForestMap, path: &Vec<NodeIndex>) -> u64 {
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path.iter().tuple_windows().fold(0, |accum, (prev, next)| {
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accum + map.graph[map.graph.find_edge(*prev, *next).unwrap()]
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})
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}
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// PROBLEM 2 solution
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fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
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0
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let mut map = ForestMap::from(input);
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map.build_graph2();
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map.simplify_graph();
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let paths = all_simple_paths::<Vec<_>, _>(&map.graph, map.indexes[&map.start], map.indexes[&map.end], 0, None)
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.collect_vec();
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let longest = paths.iter().max_by_key(|path| calc_path_length(&map, &path)).unwrap();
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longest.iter().tuple_windows().fold(0, |accum, (prev, next)| {
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accum + map.graph[map.graph.find_edge(*prev, *next).unwrap()]
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})
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}
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#[cfg(test)]
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@ -231,6 +321,6 @@ mod tests {
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#[test]
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fn problem2_example() {
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let c = Cursor::new(EXAMPLE);
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assert_eq!(problem2(c.lines()), 0);
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assert_eq!(problem2(c.lines()), 154);
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}
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}
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