Splitting a String Into Descending Consecutive Values — LeetCode 1849 Python Solution

The problem

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.

Example

Input

s = "1234"

Output

false

Explanation

There is no valid way to split s.

Python solution

class Solution:
    def splitString(self, s: str) -> bool:
        def dfs(i: int, x: int) -> bool:
            if i >= len(s):
                return True
            y = 0
            r = len(s) - 1 if x < 0 else len(s)
            for j in range(i, r):
                y = y * 10 + int(s[j])
                if (x < 0 or x - y == 1) and dfs(j + 1, y):
                    return True
            return False

        return dfs(0, -1)

Complexity

Pattern: Backtracking

Build candidates one choice at a time and abandon a branch the moment it cannot work. LeetCode 1849. Splitting a String Into Descending Consecutive Values is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Backtracking.

The backtracking guide has the Python template for the pattern and the 105 LeetCode problems that use it.

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