Number of Valid Words in a Sentence

Problem Statement - link #

A sentence consists of lowercase letters ('a' to 'z'), digits ('0' to '9'), hyphens ('-'), punctuation marks ('!', '.', and ','), and spaces (' ') only. Each sentence can be broken down into one or more tokens separated by one or more spaces ' '.

A token is a valid word if:

• It only contains lowercase letters, hyphens, and/or punctuation (no digits).
• There is at most one hyphen '-'. If present, it should be surrounded by lowercase characters ("a-b" is valid, but "-ab" and "ab-" are not valid).
• There is at most one punctuation mark. If present, it should be at the end of the token.

Examples of valid words include "a-b.", "afad", "ba-c", "a!", and "!".

Given a string sentence, return the number of valid words in sentence.

Examples #

Example 1:

Input: sentence = "cat and  dog"
Output: 3
Explanation: The valid words in the sentence are "cat", "and", and "dog".

Example 2:

Input: sentence = "!this  1-s b8d!"
Output: 0
Explanation: There are no valid words in the sentence.
"!this" is invalid because it starts with a punctuation mark.
"1-s" and "b8d" are invalid because they contain digits.

Example 3:

Input: sentence = "alice and  bob are playing stone-game10"
Output: 5
Explanation: The valid words in the sentence are "alice", "and", "bob", "are", and "playing".
"stone-game10" is invalid because it contains digits.

Example 4:

Input: sentence = "he bought 2 pencils, 3 erasers, and 1  pencil-sharpener."
Output: 6
Explanation: The valid words in the sentence are "he", "bought", "pencils,", "erasers,", "and", and "pencil-sharpener.".

Constraints #

• 1 <= sentence.length <= 1000
• sentence only contains lowercase English letters, digits, ' ', '-', '!', '.', and ','.
• There will be at least 1 token.

Solutions #

class Solution {
    bool validToken(string str) {
        int n = str.length();
        int hypen = 0;
        for(int i = 0; i < n; i++) {
            if(isdigit(str[i])) {
                return false;
            }
            if(isalpha(str[i])) {
                continue;
            }
            if(str[i] == '-') {
                if(++hypen > 1) {
                    return false;
                }
                if(i - 1 < 0 || !isalpha(str[i - 1]) || i + 1 >= n || !isalpha(str[i + 1]) ) {
                    return false;
                }
            }
            else if(i != n - 1) {
                return false;
            }
        }
        return true;
    }
public:
    int countValidWords(string sentence) {
        int res = 0;
        string word;
        stringstream ss(sentence);
        while(ss >> word) {
            res += validToken(word);
        }
        return res;
    }
};