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Leetcode 2129. Capitalize the Title

Problem Statement

You are given a string title which consists of one or more words separated by a single space, where each word consists of English letters. Capitalize the string by following the rules below:

• Return the string such that:
  • For a single letter word, it should be kept in lowercase.
  • For words with more than two letters, the first character is uppercase, and the rest are lowercase.
• Return the capitalized title as a string.

Clarifying Questions

1. Are there any non-alphabetic characters in the input string?
   • No, the input string consists only of English letters and spaces.
2. Can the input string be empty?
   • Yes, we need to handle the case where the input string is empty.
3. Should leading or trailing whitespaces be removed?
   • The input string does not contain leading or trailing whitespaces according to the problem description.
4. What about words with exactly two letters?
   • Words with exactly two letters should be converted to lowercase.

Code

public class Solution {
    public String capitalizeTitle(String title) {
        // Split the input title into words
        String[] words = title.split(" ");
        StringBuilder result = new StringBuilder();

        // Iterate through each word
        for (String word : words) {
            if (word.length() > 2) {
                // Capitalize first letter and set rest to lowercase
                result.append(Character.toUpperCase(word.charAt(0)))
                      .append(word.substring(1).toLowerCase());
            } else {
                // Convert entire word to lowercase
                result.append(word.toLowerCase());
            }
            // Append a space after each word
            result.append(" ");
        }

        // Trim the trailing space and return the result
        return result.toString().trim();
    }
}

Strategy

1. Splitting the Input: We first split the input string by spaces to get individual words.
2. Processing Each Word:
   • If the word length is greater than 2, capitalize the first letter and make the rest lowercase.
   • If the word length is 2 or less, convert the entire word to lowercase.
3. Concatenation:
   • Append each processed word to a StringBuilder.
   • Append a space after each word.
4. Trimming the Result: After processing all words, trim the trailing space to produce the correct output format.

Time Complexity

• Splitting the String: O(n), where n is the length of the input string.
• Iterating Through Words: O(w) * O(k), where w is the number of words, and k is the average length of the words. In total, this process also takes O(n) because each character is processed once.
• Overall Time Complexity: O(n), where n is the length of the input string. This is efficient and scales well with input size.

This approach ensures that we handle all the given requirements within optimal time complexity.

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