Implement SSC algorithm to finish course 2 assignment 1

data/course_2_assignment_1_test.txt

@@ -0,0 +1,11 @@
+1 4
+2 8
+3 6
+4 7
+5 2
+6 9
+7 1
+8 5
+8 6
+9 3
+9 7

src/main.rs

@@ -4,6 +4,7 @@ mod quick_sort;
 mod ssc;
 mod util;
 
+use std::cmp::min;
 use crate::util::read_to_graph;
 
 use crate::merge_sort::merge_sort_inversions;
@@ -50,10 +51,12 @@ fn c1a4() {
 
 #[allow(dead_code)]
 fn c2a1() {
+    // I have not checked in the graph file, because it has 70MB.
     // let g = read_to_directed_graph("data/course_2_assignment_1.txt").unwrap();
     let g = read_to_directed_graph("data/course_2_assignment_1_test.txt").unwrap();
-    let s = ssc(g.0, g.1);
+    let sizes = ssc(g.0, g.1);
-    println!("{:?}", s);
+    let max_size = min(sizes.len(), 5);
+    println!("{:?}", &sizes[0..max_size]);
 }
 
 fn main() {

src/ssc.rs

@@ -1,47 +1,90 @@
 use crate::util::DirectedGraph;
+use std::collections::HashMap;
 
-fn dfs(mut g: &mut DirectedGraph, node: usize, mut time: &mut usize) -> () {
+fn dfs(g: &mut DirectedGraph, node: usize, time: &mut usize) -> () {
+    let mut nodes: Vec<(usize, usize)> = vec![(node, 0)];
     g.explored[node] = true;
-    for i in 0..g.nodes[node].len() {
+
-        let j = g.nodes[node][i];
+    while nodes.len() > 0 {
-        if !g.explored[j] {
+        let (mut current_node, mut current_edge) = nodes.pop().unwrap();
-            dfs(&mut g, j, &mut time);
+        while current_edge < g.nodes[current_node].len() {
+            let next_node = g.nodes[current_node][current_edge];
+            if !g.explored[next_node] {
+                nodes.push((current_node, current_edge + 1));
+                current_node = next_node;
+                current_edge = 0;
+                g.explored[current_node] = true;
+            } else {
+                current_edge += 1;
             }
         }
         *time += 1;
-    g.time[node] = *time;
+        g.time[current_node] = *time;
+    }
 }
 
-pub fn ssc(g: DirectedGraph, mut g_dash: DirectedGraph) -> u32 {
+fn second_dfs(g: &mut DirectedGraph, node: usize, leader: usize) -> () {
-    let mut time: usize = 0;
+    let mut nodes: Vec<(usize, usize)> = vec![(node, 0)];
-    println!("ssc");
+    g.explored[node] = true;
+    g.leader[node] = leader;
+    while nodes.len() > 0 {
+        let (mut current_node, mut current_edge) = nodes.pop().unwrap();
+        while current_edge < g.nodes[current_node].len() {
+            let next_node = g.nodes[current_node][current_edge];
+            if !g.explored[next_node] {
+                nodes.push((current_node, current_edge + 1));
+                current_node = next_node;
+                current_edge = 0;
+                g.leader[current_node] = leader;
+                g.explored[current_node] = true;
+            } else {
+                current_edge += 1;
+            }
+        }
+    }
+}
 
+pub fn ssc(mut g: DirectedGraph, mut g_dash: DirectedGraph) -> Vec<usize> {
+    println!("1. start first dfs");
+    let mut time: usize = 0;
     for i in (0..g_dash.nodes.len()).rev() {
         if !g_dash.explored[i] {
             dfs(&mut g_dash, i, &mut time);
         }
     }
 
-    println!("finished first dfs");
+    println!("2. create time to index mapping");
-
     let mut time_to_index: Vec<usize> = vec![0; g.nodes.len()];
-
+    for node in 0..g_dash.nodes.len() {
-    for i in 0..g_dash.nodes.len() {
+        time_to_index[g_dash.time[node] - 1] = node;
-        time_to_index[g_dash.time[i] - 1] = i;
     }
 
-    println!("finish time look-up");
+    println!("3. start second dfs");
-
+    for time in (0..time_to_index.len()).rev() {
-    for i in (0..time_to_index.len()).rev() {
+        let node = time_to_index[time];
-        let _node = time_to_index[i];
+        if !g.explored[node] {
-        // println!("time: {:?} node: {:?}", i, node);
+            second_dfs(&mut g, node, node);
+        }
     }
 
-    println!("finished second dfs");
+    println!("4. print results");
-
+    let mut leader_size: HashMap<usize, usize> = HashMap::new();
-    for i in 0..g_dash.nodes.len() {
+    for node in 0..g.nodes.len() {
-        println!("f({})={}", i + 1, g_dash.time[i]);
+        let leader = g.leader[node];
+        let leader_size = leader_size.entry(leader).or_insert(0);
+        *leader_size += 1;
     }
 
-    0
+    let mut sizes: Vec<usize> = leader_size.values().cloned().collect();
+    sizes.sort();
+    sizes.reverse();
+
+    // For debugging the finish time and leader functions.
+    // for i in 0..g_dash.nodes.len() {
+    //     println!("f({})={}", i + 1, g_dash.time[i]);
+    // }
+    // for i in 0..g.nodes.len() {
+    // 	println!("leader({})={}", i + 1, g.leader[i] + 1);
+    // }
+    sizes
 }

src/util.rs

@@ -14,6 +14,7 @@ pub struct DirectedGraph {
     pub nodes: Vec<Vec<usize>>,
     pub explored: Vec<bool>,
     pub time: Vec<usize>,
+    pub leader: Vec<usize>,
 }
 
 pub fn read_to_vector(path: &str) -> Result<Vec<i64>, io::Error> {
@@ -59,19 +60,36 @@ pub fn read_to_graph(path: &str) -> Result<Graph, io::Error> {
     Ok(g)
 }
 
+fn get_node_size(path: &str) -> Result<usize, io::Error> {
+    let mut node_size = 0;
+    let file = File::open(path)?;
+    let br = BufReader::new(file);
+
+    for line in br.lines() {
+        let line = line?;
+        let mut nodes = line.split_whitespace();
+        let node: usize = nodes.next().unwrap().parse().unwrap();
+        if node > node_size {
+            node_size = node;
+        }
+    }
+    Ok(node_size)
+}
+
 pub fn read_to_directed_graph(path: &str) -> Result<(DirectedGraph, DirectedGraph), io::Error> {
-    const NODES: usize = 9;
+    let nodes: usize = get_node_size(path).unwrap();
-    // const NODES: usize = 875714;
     let mut g = DirectedGraph {
-        nodes: vec![vec![]; NODES],
+        nodes: vec![vec![]; nodes],
-        explored: vec![false; NODES],
+        explored: vec![false; nodes],
-        time: vec![0; NODES],
+        time: vec![0; nodes],
+        leader: vec![0; nodes],
     };
 
     let mut g_dash = DirectedGraph {
-        nodes: vec![vec![]; NODES],
+        nodes: vec![vec![]; nodes],
-        explored: vec![false; NODES],
+        explored: vec![false; nodes],
-        time: vec![0; NODES],
+        time: vec![0; nodes],
+        leader: vec![0; nodes],
     };
 
     let file = File::open(path)?;