An additive number is a string whose digits can form an additive sequence.
A valid additive sequence should contain at least three numbers. Except for the first two numbers, each subsequent number in the sequence must be the sum of the preceding two.
Given a string containing only digits, return true
if it is an additive number or false
otherwise.
Note: Numbers in the additive sequence cannot have leading zeros, so sequence 1, 2, 03
or 1, 02, 3
is invalid.
Example 1:
Input: "112358"
Output: true
Explanation:
The digits can form an additive sequence: 1, 1, 2, 3, 5, 8.
1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, 3 + 5 = 8
Example 2:
Input: "199100199"
Output: true
Explanation:
The additive sequence is: 1, 99, 100, 199.
1 + 99 = 100, 99 + 100 = 199
Constraints:
-
1 <= num.length <= 35
-
num
consists only of digits.
Follow up: How would you handle overflow for very large input integers?
SOLUTION:
class Solution:
def getSeq(self, num, i, n, a, b, ctr):
if i >= n:
return ctr >= 3
for j in range(i + 1, n + 1):
curr = int(num[i:j])
if a == None or b == None or curr == a + b:
if self.getSeq(num, j, n, b, curr, ctr + 1):
return True
if num[i] == "0":
break
return False
def isAdditiveNumber(self, num: str) -> bool:
return self.getSeq(num, 0, len(num), None, None, 0)
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