Leetcode 842. Split Array into Fibonacci Sequence

Given a string S of digits, such as S = "123456579", we can split it into a Fibonacci-like sequence [123, 456, 579].

Formally, a Fibonacci-like sequence is a list F of non-negative integers such that:

• 0 <= F[i] <= 2^31 - 1, (that is, each integer fits a 32-bit signed integer type);
• F.length >= 3;
• and F[i] + F[i+1] = F[i+2] for all 0 <= i < F.length - 2.

Also, note that when splitting the string into pieces, each piece must not have extra leading zeroes, except if the piece is the number 0 itself.

Return any Fibonacci-like sequence split from S, or return [] if it cannot be done.

Example 1:

Input: "123456579"
Output: [123,456,579]

Example 2:

Input: "11235813"
Output: [1,1,2,3,5,8,13]

Example 3:

Input: "112358130"
Output: []
Explanation: The task is impossible.

Example 4:

Input: "0123"
Output: []
Explanation: Leading zeroes are not allowed, so "01", "2", "3" is not valid.

Example 5:

Input: "1101111"
Output: [110, 1, 111]
Explanation: The output [11, 0, 11, 11] would also be accepted.

Note:

1. 1 <= S.length <= 200
2. S contains only digits.

Code (Java):

class Solution {
    public List<Integer> splitIntoFibonacci(String s) {
        List<Integer> ans = new ArrayList<>();
        if (s == null || s.length() < 3) {
            return ans;
        }

        splitIntoFibonacciHelper(0, s, ans);

        return ans;
    }

    private boolean splitIntoFibonacciHelper(int start, String s, List<Integer> curr) {
        if (start >= s.length() && curr.size() >= 3) {
            return true;
        }

        for (int i = start; i < s.length(); i++) {
            if (s.charAt(start) == '0' && i > start) {
                break;
            }
            
            long num = Long.parseLong(s.substring(start, i + 1));
            if (num > Integer.MAX_VALUE) {
                break;
            }
            
            int size = curr.size();
            if (size >= 2 && num > curr.get(size - 1) + curr.get(size - 2)) {
                break;
            }

            if (size <= 1 || num == curr.get(size - 1) + curr.get(size - 2)) {
                curr.add((int)num);
                boolean found = splitIntoFibonacciHelper(i + 1, s, curr);
                if (found) {
                    return true;
                }
                curr.remove(curr.size() - 1);
            }
        }

        return false;
    }
}