Create 357. Count Numbers with Unique Digits.py

Author: 724thomas

leetcode3/최원준/357. Count Numbers with Unique Digits.py

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+#
+
+'''
+1. 아이디어 :
+백트래킹으로 모든 경우를 구한다.
+현재 숫자에 방문하지 않은 숫자를 더한다.
+
+2. 시간복잡도 :
+    약 O(10 ** 8)
+
+3. 자료구조/알고리즘 :
+backtracking
+
+'''
+class Solution:
+    def countNumbersWithUniqueDigits(self, n: int) -> int:
+        visited = set()
+    
+        def backtrack(length, total_length):
+            if length == total_length:
+                return 1
+
+            total = 0
+
+            for i in range(10):
+                if length == 0 and i ==0:
+                    continue # 0
+                
+                if i in visited:
+                    continue
+                
+                visited.add(i)
+                total += backtrack(length+1, total_length)
+                visited.remove(i)
+
+            return total
+        
+        ans = 0
+        for length in range(n+1):
+            ans += backtrack(0, length)
+        return ans
+