Leetcode #1784: Check if Binary String Has at Most One Segment of Ones

In this guide, we solve Leetcode #1784 Check if Binary String Has at Most One Segment of Ones 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

Given a binary string s ​​​​​without leading zeros, return true​​​ if s contains at most one contiguous segment of ones. Otherwise, return false.

Quick Facts

• Difficulty: Easy
• Premium: No
• Tags: String

Intuition

We need to scan characters while tracking positions or counts.

A simple state machine keeps the logic precise.

Approach

Iterate through the string once and update the state for each character.

Use a map or array if you need fast lookups.

Steps:

• Iterate through characters.
• Maintain necessary state.
• Build or validate the output.

Example

Python Solution

Complexity

The time complexity is $O(n)$, where $n$ is the length of the string $s$. The space complexity is $O(1)$.

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.