From 415d68ac9cf41dc8ba7c3fe92595ba43b3b73513 Mon Sep 17 00:00:00 2001
From: freemjstudio <mjwoo0@naver.com>
Date: Sat, 11 Jul 2026 16:58:46 +0900
Subject: [PATCH 1/4] Add week 03 solutions

---
 combination-sum/freemjstudio.py  | 23 +++++++++++++++++++++++
 number-of-1-bits/freemjstudio.py | 15 +++++++++++++++
 valid-palindrome/freemjstudio.py | 21 +++++++++++++++++++++
 3 files changed, 59 insertions(+)
 create mode 100644 combination-sum/freemjstudio.py
 create mode 100644 number-of-1-bits/freemjstudio.py
 create mode 100644 valid-palindrome/freemjstudio.py

diff --git a/combination-sum/freemjstudio.py b/combination-sum/freemjstudio.py
new file mode 100644
index 0000000000..d6824f6949
--- /dev/null
+++ b/combination-sum/freemjstudio.py
@@ -0,0 +1,23 @@
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        answer = []
+
+        def backtracking(start_idx, total, path):
+            if target == total:
+                answer.append(path[:]) # 새로운 리스트 객체를 만들어서 저장함.
+                # 리스트가 mutable 객체이므로 path[:] 로 복사하지 않으면 path 가 바뀔 때 answer 안의 값도 바뀌게 된다.
+                return
+
+            if target < total:
+                return
+
+            for idx in range(start_idx, len(candidates)):
+                new_node = candidates[idx] # 동일한 숫자 재사용 가능함. start_idx 도 포함한다.
+                path.append(new_node)
+
+                backtracking(idx, total + new_node, path)
+                # 선택 취소
+                path.pop()
+
+        backtracking(0, 0, [])
+        return answer
diff --git a/number-of-1-bits/freemjstudio.py b/number-of-1-bits/freemjstudio.py
new file mode 100644
index 0000000000..ef95ab1dea
--- /dev/null
+++ b/number-of-1-bits/freemjstudio.py
@@ -0,0 +1,15 @@
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        binary = bin(n)
+        return binary.count("1")
+
+# bin() 을 못쓰는 경우의 풀이
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        count = 0
+
+        while n > 0:
+            count += n % 2
+            n //=2
+
+        return count
diff --git a/valid-palindrome/freemjstudio.py b/valid-palindrome/freemjstudio.py
new file mode 100644
index 0000000000..cb93b4e4e9
--- /dev/null
+++ b/valid-palindrome/freemjstudio.py
@@ -0,0 +1,21 @@
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        characters = "abcdefghijklmnopqrstuvwxyz0123456789"
+        s = s.lower()
+
+        filtered = ""
+        for ch in s:
+            if ch in characters:
+                filtered += ch
+
+        n = len(filtered)
+        left = 0
+        right = n-1
+        while left <= n//2 and right >= n//2:
+            if filtered[left] == filtered[right]:
+                left += 1
+                right -= 1
+            else:
+                return False
+
+        return True

From 5e30613e77b7a557847d4ee9c67b49a80bd1d973 Mon Sep 17 00:00:00 2001
From: freemjstudio <mjwoo0@naver.com>
Date: Sat, 11 Jul 2026 18:10:01 +0900
Subject: [PATCH 2/4] freemjstudio/decode-ways

---
 decode-ways/freemjstudio.py | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 decode-ways/freemjstudio.py

diff --git a/decode-ways/freemjstudio.py b/decode-ways/freemjstudio.py
new file mode 100644
index 0000000000..8d24a3421c
--- /dev/null
+++ b/decode-ways/freemjstudio.py
@@ -0,0 +1,20 @@
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        # invalid case
+        if s[0] == "0":
+            return 0
+
+        dp = [0] * (len(s)+1)  # 앞에서부터 i개 문자를 해석하는 방법        
+        
+        dp[0] = 1
+        dp[1] = 1
+        for i in range(2, len(s)+1):
+            one_digit = s[i-1]
+            two_digits = int(s[i-2]) * 10 + int(s[i-1])
+            if one_digit != '0': # 현재 숫자를 한자리로 해석하는 경우. (0 은 매칭되는 알파벳이 없으므로 제외)
+                dp[i] += dp[i-1]
+
+            if 10 <= two_digits <= 26: # 현재 숫자를 바로 앞자리 숫자와 묶어서 두자리로 해석하는 경우 
+                dp[i] += dp[i-2]
+         
+        return dp[len(s)]
\ No newline at end of file

From dd1d3d75bb591e15042e8347aaa6d86bed2c8fa4 Mon Sep 17 00:00:00 2001
From: freemjstudio <mjwoo0@naver.com>
Date: Sat, 11 Jul 2026 18:12:42 +0900
Subject: [PATCH 3/4] Fix decode ways formatting

---
 decode-ways/freemjstudio.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/decode-ways/freemjstudio.py b/decode-ways/freemjstudio.py
index 8d24a3421c..fb32dd1fa1 100644
--- a/decode-ways/freemjstudio.py
+++ b/decode-ways/freemjstudio.py
@@ -4,8 +4,8 @@ def numDecodings(self, s: str) -> int:
         if s[0] == "0":
             return 0
 
-        dp = [0] * (len(s)+1)  # 앞에서부터 i개 문자를 해석하는 방법        
-        
+        dp = [0] * (len(s)+1)  # 앞에서부터 i개 문자를 해석하는 방법
+
         dp[0] = 1
         dp[1] = 1
         for i in range(2, len(s)+1):
@@ -14,7 +14,7 @@ def numDecodings(self, s: str) -> int:
             if one_digit != '0': # 현재 숫자를 한자리로 해석하는 경우. (0 은 매칭되는 알파벳이 없으므로 제외)
                 dp[i] += dp[i-1]
 
-            if 10 <= two_digits <= 26: # 현재 숫자를 바로 앞자리 숫자와 묶어서 두자리로 해석하는 경우 
+            if 10 <= two_digits <= 26: # 현재 숫자를 바로 앞자리 숫자와 묶어서 두자리로 해석하는 경우
                 dp[i] += dp[i-2]
-         
-        return dp[len(s)]
\ No newline at end of file
+
+        return dp[len(s)]

From 9ee1be0c5137e6ddab9dc0bd5d21017178e680ac Mon Sep 17 00:00:00 2001
From: freemjstudio <mjwoo0@naver.com>
Date: Sat, 11 Jul 2026 18:33:56 +0900
Subject: [PATCH 4/4] freemjstudio/maximum-subarray

---
 maximum-subarray/freemjstudio.py | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 maximum-subarray/freemjstudio.py

diff --git a/maximum-subarray/freemjstudio.py b/maximum-subarray/freemjstudio.py
new file mode 100644
index 0000000000..24cbcce9ef
--- /dev/null
+++ b/maximum-subarray/freemjstudio.py
@@ -0,0 +1,14 @@
+class Solution:
+    def maxSubArray(self, nums: List[int]) -> int:
+        n = len(nums)
+        if n == 1:
+            return nums[0]
+
+        dp = [0] * n
+        dp[0] = nums[0]
+        # dp[i] = i에서 끝나는 부분 배열의 최대 합
+
+        for i in range(1, n):
+            dp[i] = max(nums[i], dp[i-1] + nums[i])
+
+        return max(dp)