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Additive number is a string whose digits can form 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.

For example:

`"112358"`

is an additive number because 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

`"199100199"`

is also an additive number, the additive sequence is: `1, 99, 100, 199`

.
1 + 99 = 100, 99 + 100 = 199

**Note:** Numbers in the additive sequence **cannot** have leading zeros, so sequence `1, 2, 03`

or `1, 02, 3`

is invalid.

Given a string containing only digits `'0'-'9'`

, write a function to determine if it's an additive number.

**Follow up:**

How would you handle overflow for very large input integers?

**Credits:**

Special thanks to @jeantimex for adding this problem and creating all test cases.

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