diff --git a/merge-two-sorted-lists/yoonthecoder.js b/merge-two-sorted-lists/yoonthecoder.js
new file mode 100644
index 000000000..7e63fa58c
--- /dev/null
+++ b/merge-two-sorted-lists/yoonthecoder.js
@@ -0,0 +1,25 @@
+var mergeTwoLists = function (list1, list2) {
+  // create a placeholder node and use it as a starting point
+  let placeholder = { val: -1, next: null };
+  let current = placeholder;
+
+  // loop through the lists until one of them is fully traversed
+  while (list1 !== null && list2 !== null) {
+    if (list1.val <= list2.val) {
+      // connect the element of list1 with the current node
+      current.next = list1;
+      // move list1 to its next node
+      list1 = list1.next;
+    } else {
+      current.next = list2;
+      list2 = list2.next;
+    }
+    // move the current pointer to the newly added node
+    current = current.next;
+  }
+  current.next = list1 !== null ? list1 : list2;
+  return placeholder.next;
+};
+
+// Time Complexity: O(n+m);
+// Space Complexity: O(1)
diff --git a/missing-number/yoonthecoder.js b/missing-number/yoonthecoder.js
new file mode 100644
index 000000000..6ce3190ce
--- /dev/null
+++ b/missing-number/yoonthecoder.js
@@ -0,0 +1,14 @@
+var missingNumber = function (nums) {
+  // store all the elemenst from nums in a Set
+  const set = new Set(nums);
+
+  // check the missing number by iterating through the index
+  for (i = 0; i <= nums.length; i++) {
+    if (!set.has(i)) {
+      return i;
+    }
+  }
+};
+
+// Time complexity: O(n);
+// Space complexity: O(n);
diff --git a/two-sum/yoonthecoder.js b/two-sum/yoonthecoder.js
new file mode 100644
index 000000000..f37002549
--- /dev/null
+++ b/two-sum/yoonthecoder.js
@@ -0,0 +1,14 @@
+var twoSum = function (nums, target) {
+  const map = new Map();
+
+  for (let i = 0; i < nums.length; i++) {
+    const complement = target - nums[i];
+    if (map.has(complement)) {
+      return [map.get(complement), i];
+    }
+    map.set(nums[i], i);
+  }
+};
+
+// Time complexity: O(n)
+// Space complexity: O(n) - hash map storage