diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index dd6d8be..757f29a 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -278,3 +278,5 @@ mod p997_find_the_town_judge;
 mod p3180_maximum_total_reward_using_operations_i;
 
 mod p3181_maximum_total_reward_using_operations_ii;
+
+mod p684_redundant_connection;
diff --git a/src/problem/p684_redundant_connection.rs b/src/problem/p684_redundant_connection.rs
new file mode 100644
index 0000000..5dc2805
--- /dev/null
+++ b/src/problem/p684_redundant_connection.rs
@@ -0,0 +1,79 @@
+/**
+ * [684] Redundant Connection
+ */
+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_connection(edges: Vec<Vec<i32>>) -> Vec<i32> {
+        let n = edges.len();
+        let mut set = UnionFindSet::new(n + 1);
+
+        let mut result = None;
+        for edge in edges.iter() {
+            let (a, b) = (edge[0] as usize, edge[1] as usize);
+
+            if set.find(a) == set.find(b) {
+                result = Some(vec![a as i32, b as i32]);
+            }
+
+            set.merge(a, b);
+        }
+
+        result.unwrap()
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_684() {
+        assert_eq!(
+            vec![2, 3],
+            Solution::find_redundant_connection(vec![vec![1, 2], vec![1, 3], vec![2, 3]])
+        );
+        assert_eq!(
+            vec![1, 4],
+            Solution::find_redundant_connection(vec![
+                vec![1, 2],
+                vec![2, 3],
+                vec![3, 4],
+                vec![1, 4],
+                vec![1, 5]
+            ])
+        );
+    }
+}