Truncate Sentence

Problem

You are given a sentence s and an integer k. You need to truncate the sentence such that it contains only the first k words. A word is defined as a substring consisting of non-space characters only.

Examples

Example 1:

Input: s = "Hello how are you Contestant", k = 4
Output: "Hello how are you"

Example 2:

Input: s = "What is the solution to this problem", k = 4
Output: "What is the solution"

Example 3:

Input: s = "chopper is not a tanuki", k = 5
Output: "chopper is not a tanuki"

Constraints

• 1 <= s.length <= 500
• k is in the range [1, the number of words in s]
• s consists of only lowercase and uppercase English letters and spaces.
• The words in s are separated by a single space.
• There are no leading or trailing spaces.

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Approach

To solve this problem, we can follow a straightforward approach:

1. Split the sentence s into a list of words.
2. Extract the first k words from this list.
3. Join these k words back into a string with spaces.

Solution

Python

class Solution:
    def truncateSentence(self, s: str, k: int) -> str:
        # Split the sentence into words
        words = s.split()
        # Get the first k words
        truncated_words = words[:k]
        # Join the first k words into a string
        truncated_sentence = " ".join(truncated_words)
        return truncated_sentence

Explanation

1. Split the sentence: We use the split() method to split the sentence into a list of words.
2. Extract first k words: We use list slicing [:k] to get the first k words.
3. Join the words: We use the join() method to join the first k words into a single string separated by spaces.

Complexity Analysis

Time Complexity: O(n)

Reason: Splitting the sentence and joining the words both take linear time, where n is the length of the sentence.

Space Complexity: O(n)

Reason: We store the words of the sentence in a list and then the truncated sentence, both of which take linear space relative to the input size.

References

LeetCode Problem: Truncate Sentence