diff --git a/contains-duplicate/jahyun-dev.rs b/contains-duplicate/jahyun-dev.rs
new file mode 100644
index 0000000000..c1ad4fa02a
--- /dev/null
+++ b/contains-duplicate/jahyun-dev.rs
@@ -0,0 +1,14 @@
+impl Solution {
+    pub fn contains_duplicate(nums: Vec<i32>) -> bool {
+        let mut nx = nums;
+        nx.sort();
+
+        for i in 1..nx.len() {
+            if nx[i] == nx[i - 1] {
+                return true;
+            }
+        }
+
+        false
+    }
+}
diff --git a/longest-consecutive-sequence/jahyun-dev.rs b/longest-consecutive-sequence/jahyun-dev.rs
new file mode 100644
index 0000000000..1665395bef
--- /dev/null
+++ b/longest-consecutive-sequence/jahyun-dev.rs
@@ -0,0 +1,29 @@
+use std::collections::HashSet;
+
+impl Solution {
+    pub fn longest_consecutive(nums: Vec<i32>) -> i32 {
+        let mut set: HashSet<i32> = HashSet::new();
+        let mut max_seq: i32 = 0;
+
+        for &n in nums.iter() {
+            set.insert(n);
+        }
+
+        for &n in set.iter() {
+            // 시작점
+            if !set.contains(&(n - 1)) {
+                let mut j = n + 1;
+                while set.contains(&j) {
+                    j += 1;
+                }
+
+                let seq = j - n;
+                if seq > max_seq {
+                    max_seq = seq
+                }
+            }
+        }
+
+        return max_seq;
+    }
+}
diff --git a/top-k-frequent-elements/jahyun-dev.rs b/top-k-frequent-elements/jahyun-dev.rs
new file mode 100644
index 0000000000..5609382563
--- /dev/null
+++ b/top-k-frequent-elements/jahyun-dev.rs
@@ -0,0 +1,16 @@
+use std::collections::HashMap;
+
+impl Solution {
+    pub fn top_k_frequent(nums: Vec<i32>, k: i32) -> Vec<i32> {
+        let mut m: HashMap<i32, i32> = HashMap::new();
+
+        for n in nums {
+            *m.entry(n).or_insert(0) += 1;
+        }
+
+        let mut items: Vec<(i32, i32)> = m.into_iter().collect();
+        items.sort_by(|a, b| b.1.cmp(&a.1));
+
+        items.into_iter().take(k as usize).map(|(n, c)| n).collect()
+    }
+}
diff --git a/two-sum/jahyun-dev.rs b/two-sum/jahyun-dev.rs
new file mode 100644
index 0000000000..c2053fdb22
--- /dev/null
+++ b/two-sum/jahyun-dev.rs
@@ -0,0 +1,37 @@
+use std::collections::HashMap;
+
+impl Solution {
+    /**
+     * Hashmap 사용 시 O(n) 시간 복잡도로 가능하다.
+     */
+    pub fn two_sum(nums: Vec<i32>, target: i32) -> Vec<i32> {
+        let mut map: HashMap<i32, i32> = HashMap::new();
+
+        for i in 0..nums.len() {
+            let v = nums[i];
+            let r = target - v;
+
+            if let Some(&j) = map.get(&r) {
+                return vec![i as i32, j as i32];
+            }
+
+            map.insert(v, i as i32);
+        }
+
+        return vec![0, 0];
+    }
+
+    pub fn two_sum_a(nums: Vec<i32>, target: i32) -> Vec<i32> {
+        let mut idx = [0i32, 2];
+
+        for i in 0..nums.len() {
+            for j in (i + 1)..nums.len() {
+                if (nums[i] + nums[j]) == target {
+                    return vec![i as i32, j as i32];
+                }
+            }
+        }
+
+        return idx.to_vec();
+    }
+}