diff --git "a/leetcode3/\353\202\250\355\232\250\354\240\225/3803. Count Residue Prefixes.py" "b/leetcode3/\353\202\250\355\232\250\354\240\225/3803. Count Residue Prefixes.py"
new file mode 100644
index 00000000..6f6b6f9b
--- /dev/null
+++ "b/leetcode3/\353\202\250\355\232\250\354\240\225/3803. Count Residue Prefixes.py"	
@@ -0,0 +1,16 @@
+class Solution:
+    def residuePrefixes(self, s: str) -> int:
+        ans = 0
+        check = set()
+
+        for i, char in enumerate(s):
+            check.add(char)
+
+            # 종류가 3가지 이상이 되면 더 계산할 필요 없음
+            if len(check) >= 3:
+                break
+            
+            # 문제에서 원하는 조건 만족할 때마다 정답 개수 += 1
+            if len(check) == (i + 1) % 3:
+                ans += 1
+        return ans
\ No newline at end of file
diff --git "a/leetcode3/\353\202\250\355\232\250\354\240\225/837. New 21 Game.py" "b/leetcode3/\353\202\250\355\232\250\354\240\225/837. New 21 Game.py"
new file mode 100644
index 00000000..2e57a97e
--- /dev/null
+++ "b/leetcode3/\353\202\250\355\232\250\354\240\225/837. New 21 Game.py"	
@@ -0,0 +1,20 @@
+# 풀이 실패
+class Solution:
+    def new21Game(self, n: int, k: int, maxPts: int) -> float:
+        if k == 0 or n >= k + maxPts:
+            return 1.0
+
+        dp = [0.0] * (n + 1)
+        dp[0] = 1.0
+        window_sum = 1.0
+
+        for i in range(1, n+1):
+            dp[i] = window_sum / maxPts
+
+            if i < k:
+                window_sum += dp[i]
+
+            if i >= maxPts and (i - maxPts) < k:
+                window_sum -= dp[i - maxPts]
+
+        return sum(dp[k:])
\ No newline at end of file