diff --git a/0073-set-matrix-zeroes/0073-set-matrix-zeroes.py b/0073-set-matrix-zeroes/0073-set-matrix-zeroes.py
index 871198b..5619b82 100644
--- a/0073-set-matrix-zeroes/0073-set-matrix-zeroes.py
+++ b/0073-set-matrix-zeroes/0073-set-matrix-zeroes.py
@@ -5,21 +5,59 @@ class Solution:
         """
         # Total complexities:
         # O(mn) time
-        # O(m+n) space
+        # O(1) space
 
-        # O(m+n) space
-        rowsToZero = set()
-        colsToZero = set()
+        # Prepare first row/col for marking
+        firstEntry = matrix[0][0]
+        # - use m[0][0] as indicator for first row and col
+        NO_ZEROES_IN_FIRST_ROW_OR_COL = 1
+        ZERO_IN_FIRST_ROW = 2
+        ZERO_IN_FIRST_COL = 3
+        ZERO_IN_FIRST_ROW_AND_COL = 4
 
-        # Find all zeros - O(mn)
-        for i in range(len(matrix)):
-            for j in range(len(matrix[i])):
+        matrix[0][0] = NO_ZEROES_IN_FIRST_ROW_OR_COL
+        if firstEntry == 0:
+            matrix[0][0] = ZERO_IN_FIRST_ROW_AND_COL
+        else:
+            print(f"cp0")
+            # Search first col for 0s - O(n)
+            for i in range(1, len(matrix)):
+                print(f"cp1")
+                if matrix[i][0] == 0:
+                    matrix[0][0] = ZERO_IN_FIRST_COL
+                    break
+
+            # Search first row for 0s - O(m)
+            for j in range(1, len(matrix[0])):
+                if matrix[0][j] == 0:
+                    if matrix[0][0] == ZERO_IN_FIRST_COL:
+                        matrix[0][0] = ZERO_IN_FIRST_ROW_AND_COL
+                    else:
+                        matrix[0][0] = ZERO_IN_FIRST_ROW 
+                    break
+
+        # Find all zeros outside the first row/col - O(mn)
+        for i in range(1, len(matrix)):
+            for j in range(1, len(matrix[i])):
                 if matrix[i][j] == 0:
-                    rowsToZero.add(i)
-                    colsToZero.add(j)
+                    # Use the first row/col as markers
+                    matrix[i][0] = 0
+                    matrix[0][j] = 0
 
-        # Zero rows and cols as needed - O(mn)
-        for i in range(len(matrix)):
-            for j in range(len(matrix[i])):
-                if i in rowsToZero or j in colsToZero:
-                    matrix[i][j] = 0 
\ No newline at end of file
+        # Zero center as needed - O(mn)
+        for i in range(1, len(matrix)):
+            for j in range(1, len(matrix[i])):
+                if matrix[i][0] == 0 or matrix[0][j] == 0:
+                    matrix[i][j] = 0
+
+        # Set first row/col if needed
+        if matrix[0][0] == ZERO_IN_FIRST_ROW or matrix[0][0] == ZERO_IN_FIRST_ROW_AND_COL:
+            for j in range(1, len(matrix[0])):
+                matrix[0][j] = 0
+            
+        if matrix[0][0] == ZERO_IN_FIRST_COL or matrix[0][0] == ZERO_IN_FIRST_ROW_AND_COL:
+            for i in range(1, len(matrix)):
+                matrix[i][0] = 0
+
+        
+        matrix[0][0] = firstEntry if matrix[0][0] == NO_ZEROES_IN_FIRST_ROW_OR_COL else 0
\ No newline at end of file