diff --git a/contains-duplicate/dongzoolee.ts b/contains-duplicate/dongzoolee.ts
new file mode 100644
index 000000000..bddc2eb20
--- /dev/null
+++ b/contains-duplicate/dongzoolee.ts
@@ -0,0 +1,4 @@
+function containsDuplicate(nums: number[]): boolean {
+  const sets = new Set<number>(nums);
+  return sets.size < nums.length;
+}
diff --git a/longest-consecutive-sequence/dongzoolee.ts b/longest-consecutive-sequence/dongzoolee.ts
new file mode 100644
index 000000000..cba805cf2
--- /dev/null
+++ b/longest-consecutive-sequence/dongzoolee.ts
@@ -0,0 +1,17 @@
+function longestConsecutive(nums: number[]): number {
+  const st = new Set(nums);
+
+  let mx = 0;
+  for (const n of st) {
+    if (st.has(n - 1)) continue;
+
+    let len = 1;
+    while (st.has(n + len)) {
+      len++;
+    }
+
+    mx = Math.max(mx, len);
+  }
+
+  return mx;
+}
diff --git a/top-k-frequent-elements/dongzoolee.ts b/top-k-frequent-elements/dongzoolee.ts
new file mode 100644
index 000000000..69ffc0bf8
--- /dev/null
+++ b/top-k-frequent-elements/dongzoolee.ts
@@ -0,0 +1,15 @@
+function topKFrequent(nums: number[], k: number): number[] {
+  const mp: { [k: number]: number } = {};
+  nums.forEach((n) => (typeof mp[n] === "number" ? mp[n]++ : (mp[n] = 1)));
+
+  const unq_nums = [...new Set(nums)];
+  unq_nums.sort((a, b) => {
+    if (mp[a] === mp[b]) {
+      return 0;
+    }
+
+    return mp[a] < mp[b] ? 1 : -1;
+  });
+
+  return unq_nums.slice(0, k);
+}
diff --git a/two-sum/dongzoolee.ts b/two-sum/dongzoolee.ts
new file mode 100644
index 000000000..34f9dd088
--- /dev/null
+++ b/two-sum/dongzoolee.ts
@@ -0,0 +1,20 @@
+function twoSum(nums: number[], target: number): number[] {
+  const sz = nums.length;
+  let l = 0,
+    r = 1,
+    sm = nums[0] + nums[1];
+
+  while (l <= sz - 2 && r <= sz - 1) {
+    sm = nums[l] + nums[r];
+
+    if (sm === target) {
+      return [l, r];
+    }
+
+    if (l === r - 1) {
+      (r++, (l = 0));
+    } else {
+      l++;
+    }
+  }
+}