TruncateSentence.cpp

// Source : https://leetcode.com/problems/truncate-sentence/
// Author : Hao Chen
// Date   : 2021-04-05

/***************************************************************************************************** 
 *
 * 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.
 ******************************************************************************************************/

class Solution {
private:
    bool isAlpha(const char& ch) {
        return (ch >='a' && ch <='z') || (ch >= 'A' && ch <='Z') ;
    }
public:
    string truncateSentence(string s, int k) {
        s += ' '; //for edge case
        bool wordStart = false;
        int i=0;
        for (; i< s.size(); i++) {
            if (!wordStart && isAlpha(s[i])) {
                wordStart = true;
            }else if (wordStart && !isAlpha(s[i])) {
                if (--k <= 0) break;
                wordStart = false;
            }
        }
        return s.substr(0, i);
    }
};