Solution Explanation: Length of Last Word

This problem asks to find the length of the last word in a given string. A "word" is defined as a maximal sequence of non-space characters. The solution uses a two-pointer approach for efficient traversal.

Approach: Reverse Traversal with Two Pointers

1. Trim Trailing Spaces: We first remove any trailing spaces from the input string s. This simplifies the logic by ensuring we don't encounter trailing spaces when searching for the last word. While not strictly necessary in all solutions, it makes the core logic cleaner.

2. Find the End of the Last Word: A pointer i starts at the end of the string (or end of the trimmed string). It moves backward until it finds a non-space character. This marks the end of the last word.

3. Find the Beginning of the Last Word: A second pointer j is initialized to the same position as i. It moves backward until it encounters a space. This marks the position before the beginning of the last word.

4. Calculate Length: The length of the last word is simply the difference between the indices i and j (i - j).

Time and Space Complexity

• Time Complexity: O(n), where n is the length of the string. We traverse the string at most twice (once for trailing spaces and once to find the word boundaries).
• Space Complexity: O(1). The algorithm uses a constant amount of extra space regardless of the input string's size. We only use a few integer variables as pointers.

Code Implementation (Python)

def lengthOfLastWord(s: str) -> int:
    """
    Finds the length of the last word in a string.
 
    Args:
        s: The input string.
 
    Returns:
        The length of the last word.
    """
    s = s.rstrip() #remove trailing spaces
    if not s: #Handle empty string case
        return 0
    n = len(s)
    i = n - 1
    while i >= 0 and s[i] == ' ':
        i -= 1
 
    j = i
    while j >= 0 and s[j] != ' ':
        j -= 1
    return i - j
 

This Python code directly implements the steps described above. Note the rstrip() method efficiently removes trailing whitespace. The if not s condition handles empty strings as a special case. Other language implementations would follow a very similar structure, adapting the string manipulation and looping constructs as needed for each language. The core logic remains the same.