LeetCode #2129 — EASY

Capitalize the Title

Build confidence with an intuition-first walkthrough focused on core interview patterns fundamentals.

The Problem

Problem Statement

You are given a string title consisting of one or more words separated by a single space, where each word consists of English letters. Capitalize the string by changing the capitalization of each word such that:

If the length of the word is 1 or 2 letters, change all letters to lowercase.
Otherwise, change the first letter to uppercase and the remaining letters to lowercase.

Return the capitalized title.

Example 1:

Input: title = "capiTalIze tHe titLe"
Output: "Capitalize The Title"
Explanation:
Since all the words have a length of at least 3, the first letter of each word is uppercase, and the remaining letters are lowercase.

Example 2:

Input: title = "First leTTeR of EACH Word"
Output: "First Letter of Each Word"
Explanation:
The word "of" has length 2, so it is all lowercase.
The remaining words have a length of at least 3, so the first letter of each remaining word is uppercase, and the remaining letters are lowercase.

Example 3:

Input: title = "i lOve leetcode"
Output: "i Love Leetcode"
Explanation:
The word "i" has length 1, so it is lowercase.
The remaining words have a length of at least 3, so the first letter of each remaining word is uppercase, and the remaining letters are lowercase.

Constraints:

1 <= title.length <= 100
title consists of words separated by a single space without any leading or trailing spaces.
Each word consists of uppercase and lowercase English letters and is non-empty.

Step 01

Brute Force Baseline

Problem summary: You are given a string title consisting of one or more words separated by a single space, where each word consists of English letters. Capitalize the string by changing the capitalization of each word such that: If the length of the word is 1 or 2 letters, change all letters to lowercase. Otherwise, change the first letter to uppercase and the remaining letters to lowercase. Return the capitalized title.

Baseline thinking

Start with the most direct exhaustive search. That gives a correctness anchor before optimizing.

Pattern signal: General problem-solving

Example 1

"capiTalIze tHe titLe"

Example 2

"First leTTeR of EACH Word"

Example 3

"i lOve leetcode"

Core Insight

What unlocks the optimal approach

Firstly, try to find all the words present in the string.
On the basis of each word's lengths, simulate the process explained in Problem.

Interview move: turn each hint into an invariant you can check after every iteration/recursion step.

Step 03

Algorithm Walkthrough

Iteration Checklist

Define state (indices, window, stack, map, DP cell, or recursion frame).
Apply one transition step and update the invariant.
Record answer candidate when condition is met.
Continue until all input is consumed.

Use the first example testcase as your mental trace to verify each transition.

Step 04

Edge Cases

Minimum Input

Single element / shortest valid input

Validate boundary behavior before entering the main loop or recursion.

Duplicates & Repeats

Repeated values / repeated states

Decide whether duplicates should be merged, skipped, or counted explicitly.

Extreme Constraints

Upper-end input sizes

Re-check complexity target against constraints to avoid time-limit issues.

Invalid / Corner Shape

Empty collections, zeros, or disconnected structures

Handle special-case structure before the core algorithm path.

Step 05

Full Annotated Code

Source-backed implementations are provided below for direct study and interview prep.

// Accepted solution for LeetCode #2129: Capitalize the Title
class Solution {
    public String capitalizeTitle(String title) {
        List<String> ans = new ArrayList<>();
        for (String s : title.split(" ")) {
            if (s.length() < 3) {
                ans.add(s.toLowerCase());
            } else {
                ans.add(s.substring(0, 1).toUpperCase() + s.substring(1).toLowerCase());
            }
        }
        return String.join(" ", ans);
    }
}

// Accepted solution for LeetCode #2129: Capitalize the Title
func capitalizeTitle(title string) string {
	title = strings.ToLower(title)
	words := strings.Split(title, " ")
	for i, s := range words {
		if len(s) > 2 {
			words[i] = strings.Title(s)
		}
	}
	return strings.Join(words, " ")
}

# Accepted solution for LeetCode #2129: Capitalize the Title
class Solution:
    def capitalizeTitle(self, title: str) -> str:
        words = [w.lower() if len(w) < 3 else w.capitalize() for w in title.split()]
        return " ".join(words)

// Accepted solution for LeetCode #2129: Capitalize the Title
struct Solution;

impl Solution {
    fn capitalize_title(title: String) -> String {
        let words: Vec<String> = title
            .split_whitespace()
            .map(Solution::capitalize_word)
            .collect();
        words.join(" ")
    }

    fn capitalize_word(s: &str) -> String {
        let n = s.len();
        let mut res = "".to_string();
        for (i, c) in s.char_indices() {
            if i == 0 {
                if n <= 2 {
                    res.push(c.to_ascii_lowercase());
                } else {
                    res.push(c.to_ascii_uppercase());
                }
            } else {
                res.push(c.to_ascii_lowercase());
            }
        }
        res
    }
}

#[test]
fn test() {
    let title = "capiTalIze tHe titLe".to_string();
    let res = "Capitalize The Title".to_string();
    assert_eq!(Solution::capitalize_title(title), res);
    let title = "First leTTeR of EACH Word".to_string();
    let res = "First Letter of Each Word".to_string();
    assert_eq!(Solution::capitalize_title(title), res);
    let title = "i lOve leetcode".to_string();
    let res = "i Love Leetcode".to_string();
    assert_eq!(Solution::capitalize_title(title), res);
}

// Accepted solution for LeetCode #2129: Capitalize the Title
function capitalizeTitle(title: string): string {
    return title
        .split(' ')
        .map(s =>
            s.length < 3 ? s.toLowerCase() : s.slice(0, 1).toUpperCase() + s.slice(1).toLowerCase(),
        )
        .join(' ');
}

Step 06

Interactive Study Demo

Use this to step through a reusable interview workflow for this problem.

Custom checkpoints (one per line)

Press Step or Run All to begin.

Step 07

Complexity Analysis

Time

O(n)

Space

O(n)

Approach Breakdown

BRUTE FORCE

O(n²) time

O(1) space

Two nested loops check every pair or subarray. The outer loop fixes a starting point, the inner loop extends or searches. For n elements this gives up to n²/2 operations. No extra space, but the quadratic time is prohibitive for large inputs.

OPTIMIZED

O(n) time

O(1) space

Most array problems have an O(n²) brute force (nested loops) and an O(n) optimal (single pass with clever state tracking). The key is identifying what information to maintain as you scan: a running max, a prefix sum, a hash map of seen values, or two pointers.

Shortcut: If you are using nested loops on an array, there is almost always an O(n) solution. Look for the right auxiliary state.

Coach Notes

Common Mistakes

Review these before coding to avoid predictable interview regressions.

Off-by-one on range boundaries

Wrong move: Loop endpoints miss first/last candidate.

Usually fails on: Fails on minimal arrays and exact-boundary answers.

Fix: Re-derive loops from inclusive/exclusive ranges before coding.