diff --git a/sik9252/BestTimeToBuyAndSellStock.js b/sik9252/BestTimeToBuyAndSellStock.js
new file mode 100644
index 0000000..bc2ef33
--- /dev/null
+++ b/sik9252/BestTimeToBuyAndSellStock.js
@@ -0,0 +1,14 @@
+var maxProfit = function (prices) {
+  let minPrice = Infinity;
+  let currentProfit = 0;
+
+  for (let i = 0; i < prices.length; i++) {
+    if (prices[i] < minPrice) {
+      minPrice = prices[i];
+    } else if (prices[i] - minPrice > currentProfit) {
+      currentProfit = prices[i] - minPrice;
+    }
+  }
+
+  return currentProfit;
+};
diff --git a/sik9252/MergeTwoSortedList.js b/sik9252/MergeTwoSortedList.js
new file mode 100644
index 0000000..66c4801
--- /dev/null
+++ b/sik9252/MergeTwoSortedList.js
@@ -0,0 +1,24 @@
+var mergeTwoLists = function (list1, list2) {
+  const start = new ListNode(-1);
+  let curr = start;
+
+  while (list1 !== null && list2 !== null) {
+    if (list1.val <= list2.val) {
+      curr.next = list1;
+      list1 = list1.next;
+    } else {
+      curr.next = list2;
+      list2 = list2.next;
+    }
+
+    curr = curr.next;
+  }
+
+  if (list1 !== null) {
+    curr.next = list1;
+  } else {
+    curr.next = list2;
+  }
+
+  return start.next;
+};
diff --git a/sik9252/TwoSum.js b/sik9252/TwoSum.js
index a260cdf..d042c68 100644
--- a/sik9252/TwoSum.js
+++ b/sik9252/TwoSum.js
@@ -1,4 +1,9 @@
-// MEMO: 편하신 언어로 작성 부탁드립니다. 해당 주석은 풀이 입력 시 지워주세요.
-function twoSum(nums, target) {
-    
-}
+var twoSum = function (nums, target) {
+  for (let i = 0; i < nums.length - 1; i++) {
+    for (let j = i + 1; j < nums.length; j++) {
+      if (nums[i] + nums[j] === target) {
+        return [i, j];
+      }
+    }
+  }
+};
diff --git a/sik9252/ValidParentheses.js b/sik9252/ValidParentheses.js
new file mode 100644
index 0000000..f6b02ad
--- /dev/null
+++ b/sik9252/ValidParentheses.js
@@ -0,0 +1,23 @@
+var isValid = function (s) {
+  if (s.length % 2 !== 0) return false;
+
+  const stack = [];
+  const map = {
+    ")": "(",
+    "]": "[",
+    "}": "{",
+  };
+
+  for (const char of s) {
+    if (map[char]) {
+      const topElement = stack.pop();
+      if (topElement !== map[char]) {
+        return false;
+      }
+    } else {
+      stack.push(char);
+    }
+  }
+
+  return stack.length === 0;
+};