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Solution: Additive Number

Explore how to apply backtracking to determine if a digit string can form an additive sequence where each number is the sum of the previous two. Understand the step-by-step recursive process, handling of leading zeros, and time-space complexity to solve this problem efficiently.

Statement

An additive number is a string whose digits can be partitioned into an additive sequence.

A valid additive sequence contains at least three numbers, where every number after the first two is equal to the sum of the two immediately preceding numbers.

Given a string, num, containing only digits, determine whether it represents an additive number. Return TRUE if a valid additive sequence can be formed from the digits of num, and FALSE otherwise.

Note: Numbers in the additive sequence cannot have leading zeros. For example, the sequences 1, 2, 03 and 1, 02, 3 are both invalid.

Constraints:

  • 11 \leq num.length ...