diff --git a/W3_diagonal_traverse.py b/W3_diagonal_traverse.py
new file mode 100644
index 00000000..4d3d2396
--- /dev/null
+++ b/W3_diagonal_traverse.py
@@ -0,0 +1,46 @@
+class Solution:
+    def findDiagonalOrder(self, mat: List[List[int]]) -> List[int]:
+        
+        if mat is None:
+            return []
+
+        
+        m = len(mat)
+        n = len(mat[0])
+
+        r = 0
+        c = 0
+
+        dir = True
+
+        result = [0] * (m * n)
+
+        for i in range(m*n):
+            result[i] = mat[r][c]
+
+            if dir:
+                if c == n-1:
+                    r+= 1
+                    dir = False
+                elif r == 0:
+                    c += 1
+                    dir = False
+                else:
+                    r -= 1
+                    c += 1
+            
+            else:
+                if r == m-1:
+                    c+= 1
+                    dir = True
+                elif c == 0:
+                    r += 1
+                    dir = True
+                else:
+                    c -= 1
+                    r += 1 
+
+        return result
+
+# Time: O(m * n)
+# Space O(1)
\ No newline at end of file
diff --git a/W3_product_except_self.py b/W3_product_except_self.py
new file mode 100644
index 00000000..dbad19b6
--- /dev/null
+++ b/W3_product_except_self.py
@@ -0,0 +1,28 @@
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+
+        result = [0] * len(nums)
+
+        if nums is None:
+            return result
+        
+        # Running product
+        rp = 1 
+        result[0] = 1
+
+        # left/forward pass
+        for i in range(1, len(nums)):
+            rp = rp * nums[i-1]
+            result[i] = rp
+        
+        rp = 1
+
+        # Right pass / backward pass
+        for i in range(len(nums) - 2, -1, -1):
+            rp = rp * nums[i+1]
+            result[i] = result[i] * rp
+
+        return result
+
+# Time complexity: O(2n) = O(N)
+# Space complexity: O(1)
\ No newline at end of file