Is Check if All A's Appears Before All B's easy or hard?

Check if All A's Appears Before All B's is classified as an Easy problem. It focuses on basic string iteration and condition checking rather than advanced algorithms or data structures.

How to solve Check if All A's Appears Before All B's in O(n)?

Iterate through the string while tracking whether a 'b' has already appeared. When you encounter 'b', set a flag. If you later see 'a' while the flag is true, the ordering rule is broken and the answer is false. If the loop finishes without violations, return true.

Check if All A's Appears Before All B's Python or Java solution

Both Python and Java implementations follow the same logic: iterate through the string and track whether a 'b' has been seen. If an 'a' appears afterward, return false. The algorithm remains O(n) time and O(1) space regardless of language.

What is the best approach for Check if All A's Appears Before All B's?

The best approach is a one-pass iteration with a boolean flag. Traverse the string once and mark when a 'b' appears. If an 'a' occurs after that point, return false immediately. This method runs in O(n) time with O(1) space and clearly expresses the ordering rule.

What data structure is used in Check if All A's Appears Before All B's?

The problem mainly uses simple string traversal and a boolean flag. No complex data structures are required. The algorithm processes characters sequentially from the input string and checks ordering conditions.

What is the time complexity of Check if All A's Appears Before All B's?

The optimal solution runs in O(n) time because it scans the string once from left to right. Each character is processed exactly once. Space complexity is O(1) since only a single flag variable is needed.

Is Check if All A's Appears Before All B's asked at Google, Amazon, or Meta?

Problems like this appear frequently in screening rounds at large tech companies because they test basic string traversal and reasoning about order constraints. While the exact problem ID may not appear, similar string validation questions are common in interviews at companies such as Amazon and Google.

Description Hints 2 Solution Video 8:30

2124. Check if All A's Appears Before All B's

Easy73.2% acceptance2 companies

Given a string s consisting of only the characters 'a' and 'b', return true if every 'a' appears before every 'b' in the string. Otherwise, return false.

Example 1:

Input: s = "aaabbb"
Output: true
Explanation:
The 'a's are at indices 0, 1, and 2, while the 'b's are at indices 3, 4, and 5.
Hence, every 'a' appears before every 'b' and we return true.

Example 2:

Input: s = "abab"
Output: false
Explanation:
There is an 'a' at index 2 and a 'b' at index 1.
Hence, not every 'a' appears before every 'b' and we return false.

Example 3:

Input: s = "bbb"
Output: true
Explanation:
There are no 'a's, hence, every 'a' appears before every 'b' and we return true.

Constraints:

1 <= s.length <= 100
s[i] is either 'a' or 'b'.

Asked at 2 companies

Microsoft Bloomberg

Topics

String

Hints open one at a time

Hint 1

You can check the opposite: check if there is a ‘b’ before an ‘a’. Then, negate and return that answer.

Hint 2

s should not have any occurrences of “ba” as a substring.

8:30

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