LeetCode 2129: Capitalize the Title – Explained with Code in C++, Java, Python & C#

If you’re tackling string manipulation problems on LeetCode, Problem 2129: Capitalize the Title is a great one to master. It challenges your understanding of word boundaries, character casing, and clean iteration—all crucial in interviews and real-world applications.

🔍 Problem Summary

You’re given a string title containing words separated by spaces. Transform it based on the following rules:

1. Words with ≤ 2 letters → Convert all characters to lowercase
2. Words with ≥ 3 letters → Capitalize the first character, lowercase the rest

Example:

Input: "capiTalIze tHe titLe"
Output: "Capitalize The Title"

🧠 Approach & Solutions in Multiple Languages

✅ C++: Two-Pointer + In-Place Modification

class Solution {
 public:
  string capitalizeTitle(string title) {
    ranges::transform(title, title.begin(), ::tolower); // Convert entire string to lowercase
    int i = 0, j = 0;
    while (j < title.length()) {
      while (j < title.length() && title[j] != ' ') j++;
      if (j - i > 2) title[i] = toupper(title[i]);
      i = j + 1;
      j++;
    }
    return title;
  }
};

• Time: O(n)
• Space: O(1)

✅ Java: Efficient String Manipulation with StringBuilder

class Solution {
  public String capitalizeTitle(String title) {
    StringBuilder sb = new StringBuilder(title.toLowerCase());
    int i = 0, j = 0;
    while (j < sb.length()) {
      while (j < sb.length() && sb.charAt(j) != ' ') j++;
      if (j - i > 2) sb.setCharAt(i, Character.toUpperCase(sb.charAt(i)));
      i = j + 1;
      j++;
    }
    return sb.toString();
  }
}

• Time: O(n)
• Space: O(n)

✅ Python: Clean and Pythonic

class Solution:
  def capitalizeTitle(self, title: str) -> str:
    return ' '.join(s.lower() if len(s) < 3 else s.capitalize() for s in title.split())

• Time: O(n)
• Space: O(n)

✅ C#: Optimized with List<char> (Approach 3)

public string CapitalizeTitle(string title) {
  List<char> result = new List<char>(title.ToLower());
  int start = 0;
  for (int i = 0; i <= result.Count; i++) {
    if (i == result.Count || result[i] == ' ') {
      int length = i - start;
      if (length > 2) result[start] = char.ToUpper(result[start]);
      start = i + 1;
    }
  }
  return new string(result.ToArray());
}

• Time: O(n)
• Space: O(n)

💡 Optimization Tips

• C++ / C#: Prefer in-place edits (e.g., using List<char> or direct string mutation) for optimal memory use.
• Java / C#: StringBuilder reduces the overhead from string concatenation.
• Python: split() and join() make concise, readable solutions.

📊 Complexity Comparison

🔗 What to Practice Next

• Leverage this logic in similar problems like:
  • Capitalizing headings
  • Title case conversion in a sentence
  • Word-based transformation using character conditions

Need more practice? Check out the LeetCode official practice portal to sharpen your skills.