1816. Truncate Sentence

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".

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.

• class Solution {
  public:
      string truncateSentence(string s, int k) {
          for(int i=0;i<s.size();++i)
              if(s[i]==' '&&--k==0)   //用单引号判断空格，只要遇见空格，--k就已经执行了
                  return s.substr(0,i);
          return s;
      }
  };

  string中很好用的截取字符串的方法substr,substr(4)表示从下标4开始，一直到结束,sunstr(4,5),表示从下标4开始，截取的长度为5

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

  Python中字符串的split方法，将字符串拆分成序列，与join方法正好相反