#1374

Easy

auto_awesomeString-driven solution strategy

LeetCode Problem Workspace

Generate a String With Characters That Have Odd Counts

Generate a string of n characters where each character appears an odd number of times, using a string-driven approach.

Problem Statement

Given an integer n, return a string of n lowercase letters where each character occurs an odd number of times. Multiple valid strings are allowed.

If n is odd, return a string consisting only of 'a's. If n is even, return a string with n-1 'a's followed by a 'b'.

Examples

Example 1

Input: n = 4

Output: "pppz"

"pppz" is a valid string since the character 'p' occurs three times and the character 'z' occurs once. Note that there are many other valid strings such as "ohhh" and "love".

Example 2

Input: n = 2

Output: "xy"

"xy" is a valid string since the characters 'x' and 'y' occur once. Note that there are many other valid strings such as "ag" and "ur".

Example 3

Input: n = 7

Output: "holasss"

Example details omitted.

Constraints

1 <= n <= 500

Solution Approach

String-driven solution

The core idea is to generate strings with odd occurrences of characters. If n is odd, use 'a' repeated n times. If n is even, use 'a' repeated n-1 times and 'b' once. This ensures that the string always satisfies the condition of odd counts for every character.

Edge case handling

Special attention should be given when n is small, as the string must still meet the condition even if n is 1. For example, when n = 1, returning 'a' is valid.

Efficient construction

By constructing the string directly with known values ('a' and 'b'), this approach minimizes unnecessary operations, ensuring an optimal solution both in time and space.

Complexity Analysis

Metric	Value
Time	Depends on the final approach
Space	Depends on the final approach

The time and space complexity are O(n) since the solution involves constructing a string of size n. The approach is optimal because no additional data structures or complex operations are required.

What Interviewers Usually Probe

Candidate demonstrates understanding of string manipulation patterns.
Candidate recognizes that the problem requires efficient handling of odd counts in string construction.
Candidate can adapt the solution for various input sizes, particularly edge cases.

Common Pitfalls or Variants

Common pitfalls

Failing to account for n = 1 and constructing the string incorrectly for small values.
Confusing the need for odd counts with simply returning any random string of length n.
Not recognizing the efficiency of directly constructing the string with specific characters ('a' and 'b').

Follow-up variants

Modify the problem to use uppercase letters instead of lowercase.
Change the problem to require multiple different characters with odd counts.
Allow characters other than 'a' and 'b' to be used to satisfy the condition.

FAQ

How do I generate a string with odd counts of characters?

To generate a string with odd counts, if n is odd, return a string with only 'a' repeated n times. If n is even, use n-1 'a's followed by a 'b'.

What is the optimal time complexity for this problem?

The optimal time complexity is O(n) because we are constructing a string of length n directly with minimal operations.

Can I use characters other than 'a' and 'b'?

While 'a' and 'b' are the simplest choice, any two distinct characters can be used to form the required odd counts.

How can I handle small values of n, like n = 1?

When n = 1, simply return 'a' as it satisfies the condition of an odd count of a single character.

What should I do if n is very large, such as 500?

For large n, the same solution applies. Construct the string directly with 'a' repeated n times if n is odd, or n-1 'a's and 1 'b' if n is even.

terminal

Solution

Solution 1: Construction

If $n$ is odd, then we can directly construct a string with $n$ `'a'` characters.

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class Solution:
    def generateTheString(self, n: int) -> str:
        return 'a' * n if n & 1 else 'a' * (n - 1) + 'b'

Continue Practicing

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