Breaking Down Strings: Calculating the Length of the Last Word
Welcome back to our series on key computational problems and solutions, designed to enhance your coding proficiency and deepen your understanding of computer algorithms. Today, we shift our focus to a common string manipulation challenge: determining the “Length of Last Word” in a given string. This task is pivotal in text processing where concise operations are often required. In previous discussions, we’ve tackled a variety of complex problems, listed below, which enhanced our approach to arrays and number manipulations. As we continue, this post explores string algorithms to bolster your skills in efficiently handling and processing text data, a fundamental skill in software development.
Previous discussions:
efficient numerical operations in “Two Sum”,
integer manipulations in “Reverse Integer”,
string reversals in “Palindrome Number”,
numeric conversions in “Roman to Integer”,
sequence comparisons in “Longest Common Prefix”,
bracket validation in “Valid Parentheses”,
list merging techniques in “Merge Two Sorted Lists”,
array deduplication in “Remove Duplicates in Place”,
efficient data restructuring in “Optimized In-Place Element Removal from Arrays”,
binary search in action “Insert Position Determination”,
Kadane’s Algorithm in “A Path to Maximum Subarray”.
About the Length of Last Word Problem
The “Length of Last Word” problem requires identifying and measuring the length of the last word in a string, which is composed of words separated by spaces. A ‘word’ is defined as any sequence of non-space characters. This challenge tests the ability to parse and process strings, particularly focusing on trailing spaces and segmentation of text into meaningful components.
Example 1:
- Input:
s = "Hello World" - Output:
5 - Explanation: The last word “World” consists of 5 letters.
Example 2:
- Input:
s = " fly me to the moon " - Output:
4 - Explanation: Despite multiple spaces, the last word “moon” has 4 characters.
Example 3:
- Input:
s = "luffy is still joyboy" - Output:
6 - Explanation: The word “joyboy” is the last word and contains 6 characters.
Solutions to the Problem
Simplest Solution: Using Built-in Functions
def lengthOfLastWord(s):
# Strip trailing spaces to ensure accurate splitting
# Split the string into words based on spaces
# -1 index directly accesses the last element of the list
return len(s.strip().split()[-1])Optimized Solution: Manual Traversal
This method involves manually parsing the string from the end to find the last word, which is more space-efficient.
def lengthOfLastWord(s):
length = 0
tail = len(s) - 1 # Start from the end of the string
# Skip trailing spaces by moving the tail pointer to the last non-space character
while tail >= 0 and s[tail] == ' ':
tail -= 1
# Count the length of the last word until a space or the beginning of the string is reached
while tail >= 0 and s[tail] != ' ':
length += 1
tail -= 1
return lengthComplexity Analysis
Simplest Solution:
- Time Complexity: O(n) — due to stripping and splitting the string, where nnn is the length of the string.
- Space Complexity: O(n) — if considering the space used for the new array created by split().
Optimized Solution:
- Time Complexity: O(n) — potentially less than nnn as it stops as soon as the last word is counted.
- Space Complexity: O(1)— uses constant space regardless of the input size.
Strip and Split: String Manipulation Methods
In programming, particularly in text processing and manipulation, certain built-in string methods provide substantial utility. Two such essential methods are strip and split, commonly used in Python and many other programming languages. Here, we explore both methods, their manual equivalents, and their strategic application in solving problems like determining the length of the last word in a string.
The strip Method
Built-in Method: The strip method in Python is used to remove leading and trailing characters (spaces by default) from a string. This method is crucial when processing raw input data, cleaning up text, or preparing strings for further manipulation. It helps in ensuring that unwanted characters do not affect the operations being performed on the string.
# Example of using strip
raw_string = " Hello World "
clean_string = raw_string.strip()
print(clean_string) # Output: "Hello World"Manual Implementation: While the built-in strip method is efficient, understanding its manual implementation can help deepen one's knowledge of string manipulation:
def manual_strip(s, chars=None):
if chars is None:
chars = ' \t\n'
start = 0
end = len(s)
# Remove leading characters
while start < end and s[start] in chars:
start += 1
# Remove trailing characters
while end > start and s[end-1] in chars:
end -= 1
# Return the stripped string
return s[start:end]
# Usage
print(manual_strip(" Hello World ")) # Output: "Hello World"The split Method
Built-in Method: The split method divides a string into a list based on a separator (default is any whitespace), often used to break down sentences into words or data into digestible parts.
# Example of using split
sentence = "Hello World"
words = sentence.split()
print(words) # Output: ['Hello', 'World']Manual Implementation: Manually implementing split involves iterating over the string and collecting slices based on the separator:
def manual_split(s, sep=None):
result = []
word = []
if sep is None:
sep = ' \t\n' # Default whitespace characters
for char in s:
if char in sep:
if word:
result.append(''.join(word))
word = []
else:
word.append(char)
if word:
result.append(''.join(word))
return result
# Usage
print(manual_split("Hello World")) # Output: ['Hello', 'World']Conclusion
The “Length of Last Word” problem serves as an excellent primer on string manipulation techniques, showcasing both straightforward and sophisticated methods for dissecting and analyzing strings efficiently. Mastery of these techniques is crucial for optimizing performance in a variety of software applications, particularly those involving textual data processing.
