diff --git a/linked-list-cycle/printjin-gmailcom.py b/linked-list-cycle/printjin-gmailcom.py
new file mode 100644
index 000000000..283f161fe
--- /dev/null
+++ b/linked-list-cycle/printjin-gmailcom.py
@@ -0,0 +1,9 @@
+class Solution:
+    def hasCycle(self, head):
+        slow = fast = head
+        while fast and fast.next:
+            slow = slow.next
+            fast = fast.next.next
+            if slow == fast:
+                return True
+        return False
diff --git a/maximum-product-subarray/printjin-gmailcom.py b/maximum-product-subarray/printjin-gmailcom.py
new file mode 100644
index 000000000..3e3908c3c
--- /dev/null
+++ b/maximum-product-subarray/printjin-gmailcom.py
@@ -0,0 +1,9 @@
+class Solution:
+    def maxProduct(self, nums):
+        max_prod = min_prod = result = nums[0]
+        for n in nums[1:]:
+            temp_max = max(n, max_prod * n, min_prod * n)
+            min_prod = min(n, max_prod * n, min_prod * n)
+            max_prod = temp_max
+            result = max(result, max_prod)
+        return result
diff --git a/minimum-window-substring/printjin-gmailcom.py b/minimum-window-substring/printjin-gmailcom.py
new file mode 100644
index 000000000..05553bbce
--- /dev/null
+++ b/minimum-window-substring/printjin-gmailcom.py
@@ -0,0 +1,19 @@
+from collections import Counter
+
+class Solution:
+    def minWindow(self, s: str, t: str) -> str:
+        need = Counter(t)
+        missing = len(t)
+        left = start = end = 0
+        for right, char in enumerate(s):
+            if need[char] > 0:
+                missing -= 1
+            need[char] -= 1
+            while missing == 0:
+                if end == 0 or right - left < end - start:
+                    start, end = left, right + 1
+                need[s[left]] += 1
+                if need[s[left]] > 0:
+                    missing += 1
+                left += 1
+        return s[start:end]
diff --git a/pacific-atlantic-water-flow/printjin-gmailcom.py b/pacific-atlantic-water-flow/printjin-gmailcom.py
new file mode 100644
index 000000000..8d6124dd4
--- /dev/null
+++ b/pacific-atlantic-water-flow/printjin-gmailcom.py
@@ -0,0 +1,25 @@
+class Solution:
+    def pacificAtlantic(self, heights):
+        if not heights:
+            return []
+        m, n = len(heights), len(heights[0])
+        pacific = [[False] * n for _ in range(m)]
+        atlantic = [[False] * n for _ in range(m)]
+        def dfs(r, c, visited):
+            visited[r][c] = True
+            for dr, dc in [(-1,0), (1,0), (0,-1), (0,1)]:
+                nr, nc = r + dr, c + dc
+                if 0 <= nr < m and 0 <= nc < n and not visited[nr][nc] and heights[nr][nc] >= heights[r][c]:
+                    dfs(nr, nc, visited)
+        for i in range(m):
+            dfs(i, 0, pacific)
+            dfs(i, n - 1, atlantic)
+        for j in range(n):
+            dfs(0, j, pacific)
+            dfs(m - 1, j, atlantic)
+        result = []
+        for r in range(m):
+            for c in range(n):
+                if pacific[r][c] and atlantic[r][c]:
+                    result.append([r, c])
+        return result
diff --git a/sum-of-two-integers/printjin-gmailcom.py b/sum-of-two-integers/printjin-gmailcom.py
new file mode 100644
index 000000000..00bc161c4
--- /dev/null
+++ b/sum-of-two-integers/printjin-gmailcom.py
@@ -0,0 +1,17 @@
+# recheck needs to be done
+
+class Solution:
+    def getSum(self, a, b):
+        MASK = 0xFFFFFFFF  # 32비트 정수를 흉내 내기 위한 마스크 (십진수로는 4294967295)
+        MAX_INT = 0x7FFFFFFF  # 32비트에서의 양수 최댓값 (2147483647)
+
+        while b != 0:
+            # a ^ b: 자리올림(carry) 없이 더한 값
+            # a & b: 같은 자리에 1이 있으면 자리올림이 생긴다는 의미
+            # (a & b) << 1: 자리올림을 왼쪽으로 이동하여 실제 올림 연산 위치로 맞춤
+            a, b = (a ^ b) & MASK, ((a & b) << 1) & MASK
+
+        # 최종적으로 a에 정답이 들어감
+        # 그런데 32비트 부호있는 정수에서는 양수 최대값이 MAX_INT
+        # a > MAX_INT라면 음수라는 뜻이므로, 보수 처리를 해줌
+        return a if a <= MAX_INT else ~(a ^ MASK)