diff --git a/leet_36.py b/leet_36.py
new file mode 100644
index 0000000..1cb51fd
--- /dev/null
+++ b/leet_36.py
@@ -0,0 +1,59 @@
+# https://leetcode.com/problems/valid-sudoku/
+# Runtime: 40 ms, faster than 98.65% of Python3 online submissions for Valid Sudoku.
+
+class Solution:
+    def isValidSudoku(self, board):
+        # validate rows
+        for row in board:
+            values = set()
+            for cell in row:
+                if cell != '.':
+                    if cell in values:
+                        return False
+                    values.add(cell)
+
+        # validate cols
+        i, j = 0, 0
+        while i < 9:
+            values = set()
+            j = 0
+            while j < 9:
+                cell = board[j][i]
+                if cell != '.':
+                    if cell in values:
+                        return False
+                    values.add(cell)
+                j += 1
+            i += 1
+        # validate districts
+        for dx in range(3):
+            cur_dx = 3 * dx
+            for dy in range(3):
+                values = set()
+                cur_dy = 3 * dy
+                for i in range(cur_dx, cur_dx + 3):
+                    for j in range(cur_dy, cur_dy + 3):
+                        cell = board[i][j]
+                        if cell != '.':
+                            if cell in values:
+                                return False
+                            values.add(cell)
+
+        return True
+
+
+if __name__ == '__main__':
+    s = Solution()
+    board = [
+        [".", ".", "4", ".", ".", ".", "6", "3", "."],
+        [".", ".", ".", ".", ".", ".", ".", ".", "."],        
+        ["5", ".", ".", ".", ".", ".", ".", "9", "."],
+        [".", ".", ".", "5", "6", ".", ".", ".", "."],
+        ["4", ".", "3", ".", ".", ".", ".", ".", "1"],
+        [".", ".", ".", "7", ".", ".", ".", ".", "."],
+        [".", ".", ".", "5", ".", ".", ".", ".", "."],
+        [".", ".", ".", ".", ".", ".", ".", ".", "."],
+        [".", ".", ".", ".", ".", ".", ".", ".", "."]
+    ]
+
+    assert s.isValidSudoku(board) == False
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