LeetCode 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".

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.

Solution

class Solution {
public:
    string truncateSentence(string s, int k) {
        int space_idx = -1;
        int num_spaces = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s[i] == ' ') {
                num_spaces++;
            }
            if (num_spaces == k) {
                space_idx = i;
                break;
            }
        }
        
        if (space_idx < 0) {
            return s;
        } else {
            return s.substr(0, space_idx);
        }
    }
};