Leetcode #1849: Splitting a String Into Descending Consecutive Values
In this guide, we solve Leetcode #1849 Splitting a String Into Descending Consecutive Values in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
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.
Quick Facts
- Difficulty: Medium
- Premium: No
- Tags: String, Backtracking, Enumeration
Intuition
We must explore combinations of choices, but many branches can be pruned early.
Backtracking enumerates valid candidates while keeping the search space under control.
Approach
Use DFS to build candidates step by step, and backtrack when constraints are violated.
Pruning keeps the exploration practical for typical constraints.
Steps:
- Define the decision tree.
- DFS through choices and backtrack.
- Prune invalid paths early.
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
The time complexity is , and the space complexity is , where is the length of the string. The space complexity is , where is the length of the string.
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.