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

[link](https://leetcode.com/problems/check-if-binary-string-has-at-most-one-segment-of-ones/)

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

#### Example 1:

Input: s = "1001"
Output: false
Explanation: The ones do not form a contiguous segment.

#### Example 2:

Input: s = "110"
Output: true

#### Constraints:

- 1 <= s.length <= 100
- s[i] is either '0' or '1'.
- s[0] is '1'.

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This question is to find if the group of `'1'` is at most one. Due to the first element of the given string is `'1'`, we can check if `'01'` is in the rest of the given string. If so, then we know that the group of `'1'` is not only one.

#### Solution 1

class Solution:
    def checkOnesSegment(self, s: str) -> bool:
        return '01' not in s
        

O(T): O(N)
O(S): O(1)