20241028 finished.

src/problem/mod.rs

@@ -280,3 +280,5 @@ mod p3180_maximum_total_reward_using_operations_i;
 mod p3181_maximum_total_reward_using_operations_ii;
 
 mod p684_redundant_connection;
+
+mod p685_redundant_connection_ii;

src/problem/p685_redundant_connection_ii.rs

@@ -0,0 +1,98 @@
+/**
+ * [685] Redundant Connection II
+ */
+pub struct Solution {}
+
+// submission codes start here
+struct UnionFindSet {
+    parents: Vec<usize>,
+}
+
+impl UnionFindSet {
+    fn new(n: usize) -> Self {
+        Self {
+            parents: (0..=n).collect(),
+        }
+    }
+
+    fn find(&mut self, n: usize) -> usize {
+        if self.parents[n] == n {
+            n
+        } else {
+            self.parents[n] = self.find(self.parents[n]);
+
+            self.parents[n]
+        }
+    }
+
+    fn merge(&mut self, a: usize, b: usize) {
+        let (a, b) = (self.find(a), self.find(b));
+
+        self.parents[a] = b;
+    }
+}
+
+impl Solution {
+    pub fn find_redundant_directed_connection(edges: Vec<Vec<i32>>) -> Vec<i32> {
+        let n = edges.len();
+        let mut set = UnionFindSet::new(n + 1);
+        let mut parents: Vec<usize> = (0..=n).collect();
+
+        let (mut conflict, mut cycle) = (usize::MAX, usize::MAX);
+
+        for (i, edge) in edges.iter().enumerate() {
+            let (first, second) = (edge[0] as usize, edge[1] as usize);
+
+            if parents[second] != second {
+                // There are the parents for second
+                conflict = i;
+            } else {
+                parents[second] = first;
+
+                if set.find(first) == set.find(second) {
+                    // There are a cycle between first and second.
+                    cycle = i;
+                } else {
+                    set.merge(first, second);
+                }
+            }
+        }
+
+        if conflict == usize::MAX {
+            edges[cycle].clone()
+        } else {
+            let result = edges[conflict].clone();
+
+            if cycle == usize::MAX {
+                result
+            } else {
+                vec![parents[result[1] as usize] as i32, result[1]]
+            }
+        }
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_685() {
+        assert_eq!(
+            vec![2, 3],
+            Solution::find_redundant_directed_connection(vec![vec![1, 2], vec![1, 3], vec![2, 3]])
+        );
+        assert_eq!(
+            vec![4, 1],
+            Solution::find_redundant_directed_connection(vec![
+                vec![1, 2],
+                vec![2, 3],
+                vec![3, 4],
+                vec![4, 1],
+                vec![1, 5]
+            ])
+        );
+    }
+}