diff --git a/best-time-to-buy-and-sell-stock/juhui-jeong.java b/best-time-to-buy-and-sell-stock/juhui-jeong.java
new file mode 100644
index 0000000000..2afdc7a2c7
--- /dev/null
+++ b/best-time-to-buy-and-sell-stock/juhui-jeong.java
@@ -0,0 +1,34 @@
+/*
+시간복잡도: O(n²)
+공간복잡도: O(1)
+class Solution {
+    public int maxProfit(int[] prices) {
+        int maxStock = 0;
+        for(int i = 0; i < prices.length; i++) {
+            for (int j = 0; j < prices.length; j++) {
+                if (i <= j) break;
+                if (prices[i] - prices[j] > maxStock) {
+                    maxStock = prices[i] - prices[j];
+                }
+            }
+        }
+        return maxStock;
+    }
+}
+ */
+// 시간복잡도: O(n)
+// 공간복잡도: O(1)
+class Solution {
+    public int maxProfit(int[] prices) {
+        int maxStock = 0;
+        int minPrice = prices[0];
+        for (int price : prices) {
+            if (price < minPrice) {
+                minPrice = price;
+            } else {
+                maxStock = Math.max(price - minPrice, maxStock);
+            }
+        }
+        return maxStock;
+    }
+}
diff --git a/group-anagrams/juhui-jeong.java b/group-anagrams/juhui-jeong.java
new file mode 100644
index 0000000000..5582fa19aa
--- /dev/null
+++ b/group-anagrams/juhui-jeong.java
@@ -0,0 +1,21 @@
+/*
+시간복잡도: O(k log k)
+공간복잡도: O(n * k) 
+*/
+class Solution {
+    public List<List<String>> groupAnagrams(String[] strs) {
+        Map<String, List<String>> map = new HashMap<>();
+
+        for (String str: strs) {
+            char[] chars = str.toCharArray();
+            Arrays.sort(chars);
+            String key = new String(chars);
+
+            if (!map.containsKey(key)) {
+                map.put(key, new ArrayList<>());
+            }
+            map.get(key).add(str);
+        }
+        return new ArrayList<>(map.values());
+    }
+}