From 9f4c8a9209acaeac3ff2f43396355dd68b569efa Mon Sep 17 00:00:00 2001
From: prograsshopper <tjalwled12@gmail.com>
Date: Fri, 8 Aug 2025 19:54:29 +0900
Subject: [PATCH 1/4] week 3: Valid Palindrome

---
 valid-palindrome/prograsshopper.py | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
 create mode 100644 valid-palindrome/prograsshopper.py

diff --git a/valid-palindrome/prograsshopper.py b/valid-palindrome/prograsshopper.py
new file mode 100644
index 000000000..631023c12
--- /dev/null
+++ b/valid-palindrome/prograsshopper.py
@@ -0,0 +1,16 @@
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        formatted_string = "".join(elem.lower() for elem in s if elem.isalnum())
+
+        # sol 1
+        return formatted_string == formatted_string[::-1]
+
+        # sol 2
+        left = 0
+        right = len(formatted_string) - 1
+        while left < right:
+            if formatted_string[left] != formatted_string[right]:
+                return False
+        left += 1
+        right -= 1
+        return True

From 9bc84ff124e0a972ad6c03597abbd3040462f0ac Mon Sep 17 00:00:00 2001
From: prograsshopper <tjalwled12@gmail.com>
Date: Sat, 9 Aug 2025 01:26:39 +0900
Subject: [PATCH 2/4] week 3: Number of 1 bits

---
 number-of-1-bits/prograsshopper.py | 10 ++++++++++
 valid-palindrome/prograsshopper.py |  2 ++
 2 files changed, 12 insertions(+)
 create mode 100644 number-of-1-bits/prograsshopper.py

diff --git a/number-of-1-bits/prograsshopper.py b/number-of-1-bits/prograsshopper.py
new file mode 100644
index 000000000..15c91c71b
--- /dev/null
+++ b/number-of-1-bits/prograsshopper.py
@@ -0,0 +1,10 @@
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        # Time complexity: O(log n)
+        output = 1
+        while n > 1:
+            remain = n % 2
+            n = n // 2
+            if remain == 1:
+                output += 1
+        return output
diff --git a/valid-palindrome/prograsshopper.py b/valid-palindrome/prograsshopper.py
index 631023c12..05d7b92cf 100644
--- a/valid-palindrome/prograsshopper.py
+++ b/valid-palindrome/prograsshopper.py
@@ -3,9 +3,11 @@ def isPalindrome(self, s: str) -> bool:
         formatted_string = "".join(elem.lower() for elem in s if elem.isalnum())
 
         # sol 1
+        # Time complexity: O(n)
         return formatted_string == formatted_string[::-1]
 
         # sol 2
+        # Time complexity: O(n)
         left = 0
         right = len(formatted_string) - 1
         while left < right:

From 744656ee32e9441160e4c67f044be5aefadcd61c Mon Sep 17 00:00:00 2001
From: prograsshopper <tjalwled12@gmail.com>
Date: Sat, 9 Aug 2025 02:04:07 +0900
Subject: [PATCH 3/4] week 3: decode ways

---
 decode-ways/prograsshopper.py | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 decode-ways/prograsshopper.py

diff --git a/decode-ways/prograsshopper.py b/decode-ways/prograsshopper.py
new file mode 100644
index 000000000..52e5df142
--- /dev/null
+++ b/decode-ways/prograsshopper.py
@@ -0,0 +1,19 @@
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        # sol 1: Time complexity O(n)
+        dp = {len(s): 1}
+
+        def dfs(start):
+            if start in dp:
+                return dp[start]
+            if s[start] == "0":
+                return 0
+            result = None
+            if start + 1 < len(s) and int(s[start:start+2]) < 27:
+                result = dfs(start+1) + dfs(start+2)
+            else:
+                result = dfs(start+1)
+            dp[start] = result
+            return result
+
+        return dfs(0)

From d7450863cecc900935ec77600686b3b340360351 Mon Sep 17 00:00:00 2001
From: prograsshopper <tjalwled12@gmail.com>
Date: Sat, 9 Aug 2025 12:44:31 +0900
Subject: [PATCH 4/4] week 3: combination sum

---
 combination-sum/prograsshopper.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
 create mode 100644 combination-sum/prograsshopper.py

diff --git a/combination-sum/prograsshopper.py b/combination-sum/prograsshopper.py
new file mode 100644
index 000000000..93a024104
--- /dev/null
+++ b/combination-sum/prograsshopper.py
@@ -0,0 +1,17 @@
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        # Time complexity: O(n ^ (T / m))
+        result = []
+
+        def dfs(remain_sum, index, path):
+            if remain_sum < 0:
+                return
+            if remain_sum == 0:
+                result.append(path)
+                return
+
+            for i in range(index, len(candidates)):
+                dfs(remain_sum - candidates[i], i, path + [candidates[i]])
+
+        dfs(target, 0, [])
+        return result