diff --git a/best-time-to-buy-and-sell-stock/Chaedie.py b/best-time-to-buy-and-sell-stock/Chaedie.py
new file mode 100644
index 000000000..99db7f549
--- /dev/null
+++ b/best-time-to-buy-and-sell-stock/Chaedie.py
@@ -0,0 +1,40 @@
+"""
+Solution: 1) 2중 포문을 돌면서 max값을 구한다.
+Time: O(n^2)
+Space: O(1)
+
+Time Limit Exceeded
+
+"""
+
+
+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+        result = 0
+        for l in range(len(prices) - 1):
+            for r in range(l + 1, len(prices)):
+                result = max(result, prices[r] - prices[l])
+
+        return result
+
+
+"""
+Solution: 
+    1) prices를 순회하면서 max_profit 을 찾는다. 
+    2) profit 은 current price - min_profit로 구한다.
+Time: O(n)
+Space: O(1)
+"""
+
+
+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+        n = len(prices)
+        max_profit = 0
+        min_price = prices[0]
+
+        for i in range(1, len(prices)):
+            profit = prices[i] - min_price
+            max_profit = max(max_profit, profit)
+            min_price = min(prices[i], min_price)
+        return max_profit
diff --git a/group-anagrams/Chaedie.py b/group-anagrams/Chaedie.py
new file mode 100644
index 000000000..43d3e29d7
--- /dev/null
+++ b/group-anagrams/Chaedie.py
@@ -0,0 +1,22 @@
+"""
+Solution: 
+    1) hash map 에 sorted_word를 키로, 해당 sorted_word 에 해당하는 요소들을 밸류로 넣습니다.
+Time: O(n^2 logn)= O(n) * O(nlogn)
+Space: O(n)
+"""
+
+
+class Solution:
+    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
+        anagram_words = defaultdict(list)
+        # dict = {sorted_word: [word, word]}
+
+        for i in range(len(strs)):
+            word = strs[i]
+            sorted_word = "".join(sorted(word))
+            anagram_words[sorted_word].append(word)
+
+        result = []
+        for arr in anagram_words.values():
+            result.append(arr)
+        return result
diff --git a/implement-trie-prefix-tree/Chaedie.py b/implement-trie-prefix-tree/Chaedie.py
new file mode 100644
index 000000000..e1de718e2
--- /dev/null
+++ b/implement-trie-prefix-tree/Chaedie.py
@@ -0,0 +1,59 @@
+"""
+Solution:
+    Trie 구조에 대해 배워보았습니다.
+    TrieNode 는 children과 ending으로 이루어져있습니다.
+    1) insert:
+        1.1) 문자열의 각 문자를 Trie 구조에 넣습니다.
+        1.2) 마지막 문자열에선 ending 을 True 로 set합니다.
+    2) search:
+        2.1) 문자열의 각 문자가 node.children 에 존재하지 않으면 False 를 반환합니다.
+        2.2) 마지막 문자가 ending 인지 판별합니다.
+    3) startsWith
+        3.1) search 와 동일하게 문자열을 순회합니다. 
+        3.2) ending 여부와 무관하게 True 를 반환합니다.
+"""
+
+
+class TrieNode:
+    def __init__(self):
+        self.children = {}
+        self.ending = False
+
+
+class Trie:
+    def __init__(self):
+        self.root = TrieNode()
+
+    def insert(self, word: str) -> None:
+        node = self.root
+
+        for char in word:
+            if char not in node.children:
+                node.children[char] = TrieNode()
+            node = node.children[char]
+        node.ending = True
+
+    def search(self, word: str) -> bool:
+        node = self.root
+
+        for char in word:
+            if char not in node.children:
+                return False
+            node = node.children[char]
+        return node.ending
+
+    def startsWith(self, prefix: str) -> bool:
+        node = self.root
+
+        for char in prefix:
+            if char not in node.children:
+                return False
+            node = node.children[char]
+        return True
+
+
+# Your Trie object will be instantiated and called as such:
+# obj = Trie()
+# obj.insert(word)
+# param_2 = obj.search(word)
+# param_3 = obj.startsWith(prefix)