Remove Vowels from a String

Remove Vowels from a String

What is this problem about?

The Remove Vowels from a String interview question asks you to take a given English string and return a new string with all vowels (a, e, i, o, u) removed. Both lowercase and uppercase vowels may need to be handled depending on the problem constraints. This is a straightforward string filtering question often used as a warm-up or screening exercise.

Why is this asked in interviews?

Amazon asks this problem as an entry-level coding screen to assess whether a candidate can write clean, concise string manipulation code. It evaluates familiarity with string iteration, character comparison, and building output strings efficiently. While simple, it tests code style — candidates who use a vowel set for O(1) lookup versus a nested condition chain show better coding instincts.

Algorithmic pattern used

The pattern is linear string traversal with set-based filtering. Define a set of vowels: {'a', 'e', 'i', 'o', 'u'}. Iterate over each character in the input string. If the character is NOT in the vowel set, include it in the result. Use a list to collect valid characters and join at the end for efficiency (avoids repeated string concatenation in languages like Python and Java).

Example explanation

Input: "leetcoding" Vowels to remove: e, e, o, i.

• l: not vowel → keep.
• e: vowel → skip.
• e: vowel → skip.
• t: keep.
• c: keep.
• o: skip.
• d: keep.
• i: skip.
• n: keep.
• g: keep.

Result: "ltcdng".

Common mistakes candidates make

• Using string concatenation in a loop instead of building a list and joining — this is O(n^2) in many languages.
• Hard-coding vowel comparisons (if c == 'a' or c == 'e' or ...) instead of using a set, making the code verbose and error-prone.
• Forgetting uppercase vowels if the problem specifies mixed-case input.
• Mutating the string in-place in languages where strings are immutable (like Python) — always build a new string.

Interview preparation tip

For the Remove Vowels from a String coding problem, the string interview pattern is the simplest possible: filter and join. Demonstrate clean code by using a vowel set and a list comprehension or equivalent. Even for easy problems, interviewers at Amazon value code clarity and efficiency. A one-liner like ''.join(c for c in s if c not in vowels) shows Python fluency and conciseness. Be ready to discuss the time and space complexity: O(n) for both.