Python program to find the longest word in a sentence

Given a string S consisting of lowercase English alphabets, the task is to print the longest word present in the given string in python.

Examples:

Input: S = “be confident and be yourself”
Output: “confident”
Explanation:
Words present in the sentence are “be”, “confident”, “and”, “be” and “yourself”. Length of each of the words are 2, 9, 3, 2, and 8 respectively.
Therefore, the longest word is “confident”.

Input: S = “geeks for geeks”
Output: “geeks”

Searching-based Approach: Refer to this article to solve this problem by performing the following steps:

• Iterate over the characters of the string.
• Check if the current character encountered is a space or end of the string is reached.
• If the current character is found to be so, update the maximum length of a word obtained.
• Finally, print the longest word obtained using substr() method.

Time Complexity: O(N) 
Auxiliary Space: O(N)

Approach using sorted() method: The idea is to split the string into separate words and store in a list. Then, sort the list in the order of increasing length using the sorted() method. Print the last string in the sorted list.

Below is the implementation of the above approach:

Python3

# Python3 program for the above approach

# Function to print the longest
# word in given sentence
def largestWord(s):

    # Sort the words in increasing
    # order of their lengths
    s = sorted(s, key = len)

    # Print last word
    print(s[-1])


# Driver Code
if __name__ == "__main__":

    # Given string
    s = "be confident and be yourself"

    # Split the string into words
    l = list(s.split(" "))

    largestWord(l)

Output

confident

Time Complexity: O(N * logN)
Auxiliary Space: O(1)

Approach using max() and split() methods:  This approach uses the max() function with the split () method to split the string into a list of words and find the longest word.

Python3

# Python3 program for the above approach

# Function to print the
# longest word in the string s


def longestword(s):

    #splitting the string into words
    s=s.split()
    # Using max() method
    print(max(s,key=len))


# Driver Code
if __name__ == "__main__":

    # Given string
    s = "be confident and be yourself"


    #calling longestword function
    longestword(s)
#This code contributed by tvsk

Output

confident

Time Complexity: O(N), N is the number of words in the input string used for iteration only once.
Auxiliary Space: O(N), N is used for creating a new list from the input string and stores it in memory.

Approach using re module:

Python3

import re

def longest_word(sentence):
    words = re.findall(r'\b\w+\b', sentence) # find all words in the sentence using regular expression
    return max(words, key=len) # return the word with the maximum length

sentence = "be confident and be yourself"
print(longest_word(sentence))

Output

confident

Time Complexity: O(N), N is the number of words in the input string used for iteration only once.
Auxiliary Space: O(N), N is used for creating a new list from the input string and stores it in memory.

Approach Using the reduce() function from the functools module: 

Algorithm:

1.Split the input string into a list of words using the split() method.
2.Initialize a variable to store the longest word as the first word in the list.
3.Iterate through the list of words and compare the length of each word to the length of the current longest word.
4.If the length of the current word is greater than the length of the current longest word, update the variable storing the longest word.
5.Return the longest word.

Python3

from functools import reduce

# function to find the longest word in a string
def longest_word(s):
    # split the string into words
    words = s.split()
    # use reduce to find the word with the maximum length
    return reduce(lambda x, y: x if len(x) > len(y) else y, words)

# example usage
s = "be confident and be yourself"
longest = longest_word(s)
print("The longest word in the string is:", longest)
#This code is contributed by Jyothi pinjala

Output

The longest word in the string is: confident

Time Complexity: O(n), where n is the total number of characters in the input string. This is because we need to iterate through each character in the string to split it into words, and then iterate through each word to find the longest one.

Space Complexity: O(m), where m is the total number of words in the input string. This is because we need to store each word in a list, and then store the longest word as a variable.