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Kotlin-based LeetCode algorithm problem solutions, regularly updated
306\. Additive Number
Medium
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?