A string is an ordered sequence of text units, but the unit depends on the language and operation. Interview solutions often reason about characters as if every visible symbol occupies one index. That assumption works for a stated ASCII contract and can fail for general Unicode. The recording introduces string operations; these notes keep their costs and text assumptions explicit.
Decide what an index means
JavaScript string indexes address UTF-16 code units. Iterating a JavaScript string with for...of yields code points, which still do not always correspond to a complete visible symbol. A base character followed by a combining mark is one example. Other languages expose different indexing and iteration APIs, so translating a loop character for character can change behavior.
Before solving a text problem, clarify the allowed input and normalization rules. Case folding, removing punctuation, and treating accented spellings as equivalent are requirements to agree on. Applying them without permission can change an identifier or make two distinct inputs compare equal. A palindrome exercise and an exact-key lookup can need different policies.
Track the cost of building the answer
Strings are immutable in languages such as JavaScript and Python. Creating a new substring or appending into a repeatedly rebuilt string can copy existing content. A loop with an apparent single assignment may therefore do increasing work. Collecting pieces and joining once can avoid repeated reconstruction under the language's usual representation model.
Reversing text also requires a choice of unit. Reversing UTF-16 units can split a surrogate pair. Reversing code points still moves combining marks independently. State a limited alphabet when that is what the exercise promises, and choose segmentation deliberately when the requirement is visible-character reversal.
Practice frequency and order separately
An anagram comparison ignores arrangement while retaining character counts. A palindrome comparison depends on symmetry in order. A permutation generator changes arrangement while retaining the original positions' contents. These are related uses of strings with different invariants.
Continue with Palindromes, Permutations, Anagrams for examples. The JavaScript preparation guide connects language behavior with interview practice. When testing a solution, include an empty input, repeated letters, and the exact text-unit boundary your stated contract supports.
Repeat a value and count the actual output
The example repeats a complete string a nonnegative number of times. Repeating ab three times gives ababab; repeating it zero times gives an empty string. If the input contains an emoji or a combining character sequence, this operation repeats that sequence intact. It does not need to decide where individual user-perceived characters begin.
That distinction keeps the example's contract narrow. A separate task such as reversing visible characters requires an explicit text model: bytes, code points, or grapheme clusters. A repetition function should not be used as evidence that every indexing operation has the same Unicode behavior across these languages.
Account for construction strategy
Let m be the size of one copy in the representation used by the language and k be the repeat count. The returned text occupies O(mk) space, and constructing its contents requires O(mk) copying work. Versions retaining k references before joining add O(k) temporary storage and loop work, including when m is zero. Implementations here use an appropriate repetition operation, builder, or growable buffer. Repeatedly copying a growing immutable prefix can do more work than the final output size suggests.
The example assumes k is nonnegative and small enough for the result to fit in memory. Test an empty string, zero repetitions, one repetition, line breaks, and multibyte text. If accepting arbitrary external requests, put a product-specific bound on output size before allocating it. A valid integer can still request an impractically large string.
C# example and implementation choices
StringBuilder appends the complete input on each iteration and then produces an immutable string. Its Length is measured in UTF-16 code units. A char index would not necessarily identify one user-perceived character, but this function does not need such an index. The nonnegative, bounded repeat count is a caller precondition rather than something the int type can establish.
Worked example
using System;
using System.Collections.Generic;
public static class RepeatTextExample {
public static string RepeatText(string text, int count) {
var output = new System.Text.StringBuilder();
for (int index = 0; index < count; index++) output.Append(text);
return output.ToString();
}
}
Continue in C#
Open Strings for the complete course explanation. The course keeps your saved programming-language choice. Use this standalone page to inspect the C# example and run it in your own local environment. Follow the original course sequence when you want the surrounding lesson context and related exercises.
The C# interview preparation guide connects these language choices with further practice and the cross-language operation reference.