From edec1f208f0bfed13e6990a6983411f3903aeee1 Mon Sep 17 00:00:00 2001
From: cy <hi@cything.io>
Date: Tue, 14 Jan 2025 01:41:10 -0500
Subject: [PATCH] implement bfs

---
 src/graph.rs | 51 +++++++++++++++++++++++++++++++++++++++++++++++++--
 src/main.rs  |  2 ++
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/src/graph.rs b/src/graph.rs
index 4998b11..903a358 100644
--- a/src/graph.rs
+++ b/src/graph.rs
@@ -1,4 +1,5 @@
 use std::rc::Rc;
+use std::collections::VecDeque;
 
 const MAXV: usize = 1000;
 
@@ -14,11 +15,21 @@ struct Edgenode {
 pub struct Graph {
     edges: Vec<Option<Rc<Edgenode>>>, // adjacency info
     degree: Vec<i32>,                 // outdegree of each vertex
-    nvertices: i32,                   // number of vertices in graph
+    nvertices: usize,                   // number of vertices in graph
     nedges: i32,                      // number of edges in graph
     directed: bool,                   // is the graph directed?
 }
 
+struct BfsState {
+    // A vertex is `discovered` the first time we visit it.
+    discovered: Vec<bool>,
+    // A vertex is `processed` after we have traversed all outgoing
+    // edges from it.
+    processed: Vec<bool>,
+    // Discovery relation
+    parent: Vec<i32>,
+}
+
 impl Graph {
     pub fn new(directed: bool) -> Self {
         Self {
@@ -46,7 +57,7 @@ impl Graph {
     }
 
     pub fn print_graph(&self) {
-        for i in 0..self.nvertices as usize {
+        for i in 0..self.nvertices {
             print!("{} -->", i);
             let mut p_opt = self.edges[i].clone();
             while let Some(p) = p_opt {
@@ -77,4 +88,40 @@ impl Graph {
             self.insert_edge(x.try_into().unwrap(), y, directed);
         }
     }
+
+    pub fn bfs(&self, start: usize) {
+        let mut state = BfsState::new();
+        let mut q: VecDeque<usize> = VecDeque::new();
+        q.push_back(start);
+        state.discovered[start] = true;
+
+        while let Some(v) = q.pop_front() {
+            println!("process_vertex_early: {:?}", v);
+            state.processed[v] = true;
+            let mut p_opt = &self.edges[v];
+            while let Some(p) = p_opt {
+                let y: usize = p.y.try_into().unwrap();
+                if !state.processed[y] || self.directed {
+                    println!("process edge ({:?},{:?})", v, y);
+                }
+                if !state.discovered[y] {
+                    q.push_back(y);
+                    state.discovered[y] = true;
+                    state.parent[y] = v.try_into().unwrap();
+                }
+                p_opt = &p.next;
+            }
+            println!("procesess vertex late: {:?}", v);
+        }
+    }
+}
+
+impl BfsState {
+    pub fn new() -> Self {
+        BfsState {
+            discovered: vec![false; MAXV],
+            processed: vec![false; MAXV],
+            parent: vec![-1; MAXV],
+        }
+    }
 }
diff --git a/src/main.rs b/src/main.rs
index b4394c1..69d1777 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -21,4 +21,6 @@ fn main() {
                 5 2";
     graph.read_graph(data.to_string());
     graph.print_graph();
+
+    graph.bfs(1);
 }