Question

1816. Truncate Sentence

中文文档

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:
  def truncateSentence(self, s: str, k: int) -> str:
    return ' '.join(s.split()[:k])

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;
  }
};

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;
};

Solution 2

class Solution:
  def truncateSentence(self, s: str, k: int) -> str:
    for i, c in enumerate(s):
      k -= c == ' '
      if k == 0:
        return s[:i]
    return s