1849. Splitting a String Into Descending Consecutive Values

You are given a string s that consists of only digits.

Check if we can split s into two or more non-empty substrings such that the numerical values of the substrings are in descending order and the difference between numerical values of every two adjacent substrings is equal to 1.

• For example, the string s = “0090089” can be split into [“0090”, “089”] with numerical values [90,89]. The values are in descending order and adjacent values differ by 1, so this way is valid.
• Another example, the string s = “001” can be split into [“0”, “01”], [“00”, “1”], or [“0”, “0”, “1”]. However all the ways are invalid because they have numerical values [0,1], [0,1], and [0,0,1] respectively, all of which are not in descending order.

Return true if it is possible to split s​​​​​​ as described above, or false otherwise.

A substring is a contiguous sequence of characters in a string.

class Solution {
    bool isDescendingOrder(string& s, int pos, unsigned long long prev) {
        if(pos == s.length()) return true;
        unsigned long long val = 0;
        for(int i = pos; i < s.length(); i++) {
            val = val * 10 + (s[i] & 0b1111);
            if(val > prev) return false;
            if(val + 1 == prev && isDescendingOrder(s, i + 1, val)) return true;
        }
        return false;
    }
public:
    bool splitString(string s) {
        unsigned long long val = 0;
        for(int i = 0; i < s.length() - 1; i++) {
            val = val * 10 + (s[i] & 0b1111);
            if(isDescendingOrder(s, i + 1, val)) return true;
        }
        return false;
    }
};