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authorjack <0x6A73@pm.me>2024-06-14 13:13:15 -0600
committerjack <0x6A73@pm.me>2024-06-14 13:13:15 -0600
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tree96df922dae2a5073d9a50ea70c7aae6aa37e3ebe /count_special_integers.py
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+# 2376. Count Special Integers
+from math import perm
+
+"""
+we call a positive integer special if all of its digits are distinct. given a
+positive integer 'n', return the number of special integers that belong to
+the interval '[1, n]'
+"""
+
+
+class Solution(object):
+ def countSpecialNumbers(self, n):
+ """
+ :type n: int
+ :rtype: int
+ """
+ l = list(map(int, str(n + 1)))
+ m = len(l)
+ ans = sum(9 * perm(9, i) for i in range(m - 1))
+ s = set()
+ for i, x in enumerate(l):
+ for y in range(i == 0, x):
+ if y not in s:
+ ans += perm(9 - i, m - i - 1)
+ if x in s:
+ break
+ s.add(x)
+ return ans
+
+
+if __name__ == "__main__":
+ obj = Solution()
+ print(obj.countSpecialNumbers(20))
+ print(obj.countSpecialNumbers(5))
+ print(obj.countSpecialNumbers(135))