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1816. Truncate Sentence

Description

A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each of the words consists of only uppercase and lowercase English letters (no punctuation).

  • For example, "Hello World", "HELLO", and "hello world hello world" are all sentences.

You are given a sentence s​​​​​​ and an integer k​​​​​​. You want to truncate s​​​​​​ such that it contains only the first k​​​​​​ words. Return s​​​​​​ after truncating it.

 

Example 1:

 Input: s = "Hello how are you Contestant", k = 4 Output: "Hello how are you" Explanation: The words in s are ["Hello", "how" "are", "you", "Contestant"]. The first 4 words are ["Hello", "how", "are", "you"]. Hence, you should return "Hello how are you".

Example 2:

 Input: s = "What is the solution to this problem", k = 4 Output: "What is the solution" Explanation: The words in s are ["What", "is" "the", "solution", "to", "this", "problem"]. The first 4 words are ["What", "is", "the", "solution"]. Hence, you should return "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 consist 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.

Solutions

Solution 1: Simulation

We traverse the string $s$ from the beginning. For the current character $s[i]$, if it is a space, we decrement $k$. When $k$ becomes $0$, it means that we have extracted $k$ words, so we return the substring $s[0..i)$.

After the traversal, we return $s$.

The time complexity is $O(n)$, where $n$ is the length of the string $s$. Ignoring the space complexity of the answer, the space complexity is $O(1)$.

  • class Solution { public String truncateSentence(String s, int k) { for (int i = 0; i < s.length(); ++i) { if (s.charAt(i) == ' ' && (--k) == 0) { return s.substring(0, i); } } return s; } } 
  • class Solution { public: string truncateSentence(string s, int k) { for (int i = 0; i < s.size(); ++i) { if (s[i] == ' ' && (--k) == 0) { return s.substr(0, i); } } return s; } }; 
  • class Solution: def truncateSentence(self, s: str, k: int) -> str: return ' '.join(s.split()[:k]) 
  • func truncateSentence(s string, k int) string { for i, c := range s { if c == ' ' { k-- } if k == 0 { return s[:i] } } return s } 
  • function truncateSentence(s: string, k: number): string { for (let i = 0; i < s.length; ++i) { if (s[i] === ' ' && --k === 0) { return s.slice(0, i); } } return s; } 
  • /** * @param {string} s * @param {number} k * @return {string} */ var truncateSentence = function (s, k) { for (let i = 0; i < s.length; ++i) { if (s[i] === ' ' && --k === 0) { return s.slice(0, i); } } return s; };

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