Added Course Schedule

Author: ryanoneill

src/course_schedule.rs

@@ -1,3 +1,7 @@
+use std::collections::HashMap;
+use std::collections::HashSet;
+use std::collections::VecDeque;
+
 /// There are a total of `numCourses` courses you have to take, labeled from
 /// `0` to `numCourses - 1`. You are given an array `prerequisites` where
 /// `prerequisites[i] = [ai, bi]` indicates that you must take course `bi`
@@ -11,9 +15,53 @@ struct Solution;
 
 impl Solution {
 
-    // TODO: Implement
-    pub fn can_finish(_num_courses: i32, _prerequisites: Vec<Vec<i32>>) -> bool {
-        false
+    pub fn can_finish(num_courses: i32, prerequisites: Vec<Vec<i32>>) -> bool {
+        let n = num_courses as usize;
+
+        let mut in_degrees = vec![0; n];
+        let mut out_degrees = vec![0; n];
+        let mut prereq_for = HashMap::new();
+
+        for p in prerequisites {
+            let prereq = p[1] as usize;
+            let for_class = p[0] as usize;
+            prereq_for
+                .entry(prereq)
+                .or_insert(HashSet::new())
+                .insert(for_class);
+            out_degrees[prereq] += 1;
+            in_degrees[for_class] += 1;
+        }
+
+        let mut seen = HashSet::new();
+        let mut queue = VecDeque::new();
+
+        for i in 0..n {
+            if in_degrees[i] == 0 {
+                queue.push_back(i);
+                seen.insert(i);
+            }
+        }
+
+        while !queue.is_empty() {
+            let current = queue.pop_front().unwrap();
+            match prereq_for.get(&current) {
+                Some(classes) => {
+                    for &class in classes {
+                        if !seen.contains(&class) {
+                            in_degrees[class] -= 1;
+                            if in_degrees[class] == 0 {
+                                queue.push_back(class);
+                                seen.insert(class);
+                            }
+                        }
+                    }
+                }
+                None => { }
+            }
+        }
+
+        seen.len() == n
     }
 
 }
@@ -22,7 +70,6 @@ impl Solution {
 mod tests {
     use super::Solution;
 
-    #[ignore]
     #[test]
     fn example_1() {
         let num_courses = 2;
@@ -31,7 +78,6 @@ mod tests {
         assert!(result);
     }
 
-    #[ignore]
     #[test]
     fn example_2() {
         let num_courses = 2;
@@ -40,4 +86,16 @@ mod tests {
         assert!(!result);
     }
 
+    #[test]
+    fn sedgewick_example() {
+        let num_courses = 13;
+        let prerequisites = vec![
+            vec![0,2], vec![1,0], vec![3,2], vec![4,5], vec![4,6], vec![5,0], vec![5,3],
+            vec![6,7], vec![7,8], vec![9,6], vec![10,9], vec![11,9], vec![12,9], vec![12,11]
+        ];
+
+        let result = Solution::can_finish(num_courses, prerequisites);
+        assert!(result);
+    }
+
 }

src/lib.rs

@@ -99,7 +99,7 @@ pub mod number_of_islands; // 200
 pub mod happy_number; // 202
 
 pub mod reverse_linked_list; // 206
-pub mod course_schedule; // 207
+pub mod course_schedule; // 207 ✓
 
 pub mod contains_duplicate; // 217