diff --git a/combination-sum/printjin-gmailcom.py b/combination-sum/printjin-gmailcom.py
new file mode 100644
index 000000000..94afe2604
--- /dev/null
+++ b/combination-sum/printjin-gmailcom.py
@@ -0,0 +1,15 @@
+class Solution:
+    def combinationSum(self, candidates, target):
+        output, nums = [], []
+        def dfs(start, total):
+            if total > target:
+                return
+            if total == target:
+                return output.append(nums[:])
+            for i in range(start, len(candidates)):
+                num = candidates[i]
+                nums.append(num)
+                dfs(i, total + num)
+                nums.pop()
+        dfs(0, 0)
+        return output
diff --git a/decode-ways/printjin-gmailcom.py b/decode-ways/printjin-gmailcom.py
new file mode 100644
index 000000000..ffec156e3
--- /dev/null
+++ b/decode-ways/printjin-gmailcom.py
@@ -0,0 +1,13 @@
+class Solution:
+    def numDecodings(self, s):
+        if not s:
+            return 0
+        dp = [0] * (len(s) + 1)
+        dp[0] = 1 
+        dp[1] = 1 if s[0] != '0' else 0 
+        for i in range(2, len(s) + 1):
+            if '1' <= s[i - 1] <= '9':
+                dp[i] += dp[i - 1]
+            if '10' <= s[i - 2:i] <= '26':
+                dp[i] += dp[i - 2]
+        return dp[len(s)]  
diff --git a/maximum-subarray/printjin-gmailcom.py b/maximum-subarray/printjin-gmailcom.py
new file mode 100644
index 000000000..4e420ab67
--- /dev/null
+++ b/maximum-subarray/printjin-gmailcom.py
@@ -0,0 +1,7 @@
+class Solution:
+    def maxSubArray(self, nums):
+        max_sum = current_sum = nums[0]
+        for num in nums[1:]:
+            current_sum = max(num, current_sum + num)
+            max_sum = max(max_sum, current_sum)
+        return max_sum
diff --git a/number-of-1-bits/printjin-gmailcom.py b/number-of-1-bits/printjin-gmailcom.py
new file mode 100644
index 000000000..13a6eb9ba
--- /dev/null
+++ b/number-of-1-bits/printjin-gmailcom.py
@@ -0,0 +1,7 @@
+class Solution:
+    def hammingWeight(self, n):
+        cnt = 0
+        while n > 0:
+            cnt += n % 2
+            n //= 2
+        return cnt
diff --git a/valid-palindrome/printjin-gmailcom.py b/valid-palindrome/printjin-gmailcom.py
new file mode 100644
index 000000000..a58734637
--- /dev/null
+++ b/valid-palindrome/printjin-gmailcom.py
@@ -0,0 +1,4 @@
+class Solution:
+    def isPalindrome(self, s):
+        cleaned = [c.lower() for c in s if c.isalnum()]
+        return cleaned == cleaned[::-1]