1784. Check if Binary String Has at Most One Segment of Ones 

Description

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'.

Solutions

Solution 1: No '1' After '0'

Notice that the string $s$ does not contain leading zeros, which means $s$ starts with '1'.

If the string $s$ contains the substring "01", then $s$ must be a string like "1...01...", in which case $s$ has at least two consecutive '1' segments, which does not satisfy the problem condition, so we return false.

If the string $s$ does not contain the substring "01", then $s$ can only be a string like "1..1000...", in which case $s$ has only one consecutive '1' segment, which satisfies the problem condition, so we return true.

Therefore, we only need to judge whether the string $s$ contains the substring "01".

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

Python3

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

Java

class Solution {
    public boolean checkOnesSegment(String s) {
        return !s.contains("01");
    }
}

C++

class Solution {
public:
    bool checkOnesSegment(string s) {
        return s.find("01") == -1;
    }
};

Go

func checkOnesSegment(s string) bool {
	return !strings.Contains(s, "01")
}

TypeScript

function checkOnesSegment(s: string): boolean {
    let pre = s[0];
    for (const c of s) {
        if (pre !== c && c === '1') {
            return false;
        }
        pre = c;
    }
    return true;
}

Rust

impl Solution {
    pub fn check_ones_segment(s: String) -> bool {
        !s.contains("01")
    }
}

Solution 2

TypeScript

function checkOnesSegment(s: string): boolean {
    return !s.includes('01');
}