Given an integer n represented as a string, return the smallest good base of n.
We call k >= 2 a good base of n, if all digits of n base k are 1's.
Example 1:
Input: n = "13"
Output: "3"
Explanation: 13 base 3 is 111.
Example 2:
Input: n = "4681"
Output: "8"
Explanation: 4681 base 8 is 11111.
Example 3:
Input: n = "1000000000000000000"
Output: "999999999999999999"
Explanation: 1000000000000000000 base 999999999999999999 is 11.
Constraints:
-
nis an integer in the range[3, 1018]. -
ndoes not contain any leading zeros.
SOLUTION:
class Solution:
def getNum(self, base, l):
val = 0
for _ in range(l):
val = base * val + 1
return val
def smallestGoodBase(self, n: str) -> str:
n = int(n)
for l in range(len("{:b}".format(n)), 1, -1):
beg = 2
end = n - 1
while beg <= end:
mid = (beg + end) // 2
val = self.getNum(mid, l)
if val == n:
return str(mid)
elif beg == end:
break
elif val < n:
beg = mid + 1
else:
end = mid
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