From 12d35cb72e5cd0db69b58dfc269f55be9ec9a417 Mon Sep 17 00:00:00 2001
From: kimseongeun <sekim520@gmail.com>
Date: Wed, 16 Apr 2025 22:47:24 +0900
Subject: [PATCH 1/4] week 3 solutions

---
 number-of-1-bits/i-mprovising.py |  9 +++++++++
 valid-palindrome/i-mprovising.py | 13 +++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 number-of-1-bits/i-mprovising.py
 create mode 100644 valid-palindrome/i-mprovising.py

diff --git a/number-of-1-bits/i-mprovising.py b/number-of-1-bits/i-mprovising.py
new file mode 100644
index 000000000..3bff8cf22
--- /dev/null
+++ b/number-of-1-bits/i-mprovising.py
@@ -0,0 +1,9 @@
+"""
+Time complexity O(n)
+Space complexity O(1)
+"""
+
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+        return bin(n).count('1')
+        
\ No newline at end of file
diff --git a/valid-palindrome/i-mprovising.py b/valid-palindrome/i-mprovising.py
new file mode 100644
index 000000000..bc33565e7
--- /dev/null
+++ b/valid-palindrome/i-mprovising.py
@@ -0,0 +1,13 @@
+"""
+Time complexity O(n)
+Space complexity O(n)
+"""
+
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        # preprocessing
+        string = [c for c in s.lower() if c.isalnum()]
+
+        if string == [c for c in string[::-1]]:
+            return True
+        return False

From 6498391b2037346f09b75cc870d9263048c17d40 Mon Sep 17 00:00:00 2001
From: kimseongeun <sekim520@gmail.com>
Date: Wed, 16 Apr 2025 22:49:55 +0900
Subject: [PATCH 2/4] fix number-of-1-bits linelint

---
 number-of-1-bits/i-mprovising.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/number-of-1-bits/i-mprovising.py b/number-of-1-bits/i-mprovising.py
index 3bff8cf22..9494d565d 100644
--- a/number-of-1-bits/i-mprovising.py
+++ b/number-of-1-bits/i-mprovising.py
@@ -6,4 +6,3 @@
 class Solution:
     def hammingWeight(self, n: int) -> int:
         return bin(n).count('1')
-        
\ No newline at end of file

From eea1160f49aa4256433881fc8e036dc5e876619c Mon Sep 17 00:00:00 2001
From: kimseongeun <sekim520@gmail.com>
Date: Wed, 16 Apr 2025 23:59:06 +0900
Subject: [PATCH 3/4] decode-ways solution

---
 decode-ways/i-mprovising.py | 40 +++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 decode-ways/i-mprovising.py

diff --git a/decode-ways/i-mprovising.py b/decode-ways/i-mprovising.py
new file mode 100644
index 000000000..4e4d694c3
--- /dev/null
+++ b/decode-ways/i-mprovising.py
@@ -0,0 +1,40 @@
+"""
+Time complexity O(n)
+Space complexity O(1)
+
+Dynamic programming
+"""
+
+
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        if s[0] == '0':
+            return 0
+        n = len(s)
+        if n == 1:
+            return 1
+        tmp = int(s[:2])
+        dp = [1, 1]
+        if 11 <= tmp <= 26:
+            if tmp != 20:
+                dp = [1, 2]
+        elif s[1] == '0':
+            if tmp not in [10, 20]:
+                return 0
+        if n == 2:
+            return dp[-1]
+        
+        for i in range(2, n):
+            if s[i] == '0':
+                if s[i-1] in ['1', '2']:
+                    cur = dp[0]
+                else:
+                    return 0
+            else:
+                cur = dp[1]
+                tmp = int(s[i-1:i+1])
+                if (11 <= tmp <= 26) and (tmp != 20):
+                    cur += dp[0]
+            dp = [dp[1], cur]
+
+        return dp[-1]

From 83139c19db2b5843d2af757be5b3160bf07f812a Mon Sep 17 00:00:00 2001
From: kimseongeun <sekim520@gmail.com>
Date: Sat, 19 Apr 2025 15:31:59 +0900
Subject: [PATCH 4/4] add combination sum, maximum subarray solution

---
 combination-sum/i-mprovising.py  | 19 +++++++++++++++++++
 maximum-subarray/i-mprovising.py | 18 ++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 combination-sum/i-mprovising.py
 create mode 100644 maximum-subarray/i-mprovising.py

diff --git a/combination-sum/i-mprovising.py b/combination-sum/i-mprovising.py
new file mode 100644
index 000000000..e1f4adbab
--- /dev/null
+++ b/combination-sum/i-mprovising.py
@@ -0,0 +1,19 @@
+"""
+Time complexity O(c*t)
+Space complexity O(c*t)
+
+Dynamic programming
+"""
+
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        # init dp array
+        dp = [[] for _ in range(target+1)] # dp[i] : combinations to sum to i
+        dp[0] = [[]]
+
+        for candidate in candidates:
+            for num in range(candidate, target+1):
+                for comb in dp[num-candidate]:
+                    dp[num].append(comb + [candidate])
+        
+        return dp[-1]
diff --git a/maximum-subarray/i-mprovising.py b/maximum-subarray/i-mprovising.py
new file mode 100644
index 000000000..1e9cfeb2c
--- /dev/null
+++ b/maximum-subarray/i-mprovising.py
@@ -0,0 +1,18 @@
+"""
+Time complexity O(n)
+Space complexity O(n)
+
+Dynamic programming
+"""
+
+
+class Solution:
+    def maxSubArray(self, nums: List[int]) -> int:
+        n = len(nums)
+        dp = [0 for _ in range(n)]
+        dp[0] = nums[0]
+
+        for i in range(1, n):
+            dp[i] = max(dp[i-1]+nums[i], nums[i])
+        
+        return max(dp)