Add problem 2360: Longest Cycle in a Graph

src/lib.rs

@@ -1750,6 +1750,7 @@ pub mod problem_2352_equal_row_and_column_pairs;
 pub mod problem_2353_design_a_food_rating_system;
 pub mod problem_2357_make_array_zero_by_subtracting_equal_amounts;
 pub mod problem_2358_maximum_number_of_groups_entering_a_competition;
+pub mod problem_2360_longest_cycle_in_a_graph;
 
 #[cfg(test)]
 mod test_utilities;

src/problem_2360_longest_cycle_in_a_graph/iterative.rs

@@ -0,0 +1,67 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+use std::mem;
+
+impl Solution {
+    pub fn longest_cycle(edges: Vec<i32>) -> i32 {
+        const MAX_BIT: u32 = 1 << 31;
+
+        let mut edges = edges;
+        let n = edges.len();
+        let mut result = 0;
+        let mut current_id = MAX_BIT - 1;
+
+        for i in 0..n {
+            let mut state = &mut edges[i];
+
+            if ((*state + 1) as u32) < MAX_BIT {
+                current_id += 1;
+
+                let start_id = current_id;
+
+                loop {
+                    let next = mem::replace(state, current_id as _) as usize;
+
+                    if let Some(next_state) = edges.get_mut(next) {
+                        if ((*next_state + 1) as u32) < MAX_BIT {
+                            state = next_state;
+                            current_id += 1;
+
+                            continue;
+                        }
+
+                        if *next_state as u32 >= start_id {
+                            result = result.max(current_id - *next_state as u32);
+                        }
+                    }
+
+                    break;
+                }
+            }
+        }
+
+        if result == 0 {
+            -1
+        } else {
+            (result + 1) as _
+        }
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn longest_cycle(edges: Vec<i32>) -> i32 {
+        Self::longest_cycle(edges)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_2360_longest_cycle_in_a_graph/mod.rs

@@ -0,0 +1,23 @@
+pub mod iterative;
+
+pub trait Solution {
+    fn longest_cycle(edges: Vec<i32>) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            (&[3, 3, 4, 2, 3] as &[_], 3),
+            (&[2, -1, 3, 1], -1),
+            (&[3, 3, 4, 2, 3], 3),
+            (&[4, 3, 3, 4, 7, 2, 3, 3], 3),
+        ];
+
+        for (edges, expected) in test_cases {
+            assert_eq!(S::longest_cycle(edges.to_vec()), expected);
+        }
+    }
+}