Count Sentences and Words

Given a string s representing a text, count the number of sentences and words in it.

• A sentence is a sequence of space-separated tokens ending with one or more of ., !, or ?. If the text does not end with a sentence-ending punctuation mark, the last sequence of tokens is also considered a sentence.
• A word is a maximal sequence of alphabetic characters (a-z or A-Z).

Return an array [sentenceCount, wordCount].

Examples:

Input: s = "Sentences"
Output: [1, 1]
Explanation: There is one sentence and one word in the given text.

Input: s = "many??? Sentences are"
Output: [2, 3]
Explanation: The text contains two sentences: "many???", "Sentences are". The words are: "many", "Sentences", "are". Hence, the answer is [2, 3].

[Expected Approach] Using Single Traversal - O(|s|) Time and O(1) Space

The idea is to scan the text once and maintain two states: whether we are inside a word and whether we are inside a sentence.

Whenever an alphabetic character starts after a non-word position, we count a new word. Whenever a non-space and non-punctuation character starts after a sentence break, we count a new sentence. If ., !, or ? appears, the current sentence ends.

Let us understand with example:

Input: s = "many??? Sentences are"

• many starts a word and a sentence.
• ? ends the sentence.
• Extra ? do not add new words.
• Sentences starts another sentence and word.
• are starts another word.

So, sentences = 2 and words = 3.

#include <iostream>
#include <vector>
#include <cctype>
using namespace std;

vector<int> sentenceWord(string& s) {
    int sentenceCount = 0;
    int wordCount = 0;

    bool inSentence = false;
    bool inWord = false;

    for (char ch : s) {
        if (ch == '.' || ch == '!' || ch == '?') {
            inSentence = false;
            inWord = false;
        } else if (ch == ' ') {
            inWord = false;
        } else {
            // Start of a new word.
            if (!inWord && isalpha(ch)) {
                inWord = true;
                wordCount++;
            }

            // Start of a new sentence.
            if (!inSentence) {
                inSentence = true;
                sentenceCount++;
            }
        }
    }

    return {sentenceCount, wordCount};
}

void printVector(vector<int>& res) {
    cout << "[" << res[0] << ", " << res[1] << "]" << endl;
}

int main() {
    string s = "Sentences";
    vector<int> res = sentenceWord(s);
    printVector(res);

    s = "many??? Sentences are";
    res = sentenceWord(s);
    printVector(res);

    return 0;
}

import java.util.ArrayList;

public class GFG {
    static ArrayList<Integer> sentenceWord(String s) {
        int sentenceCount = 0;
        int wordCount = 0;

        boolean inSentence = false;
        boolean inWord = false;

        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);

            if (ch == '.' || ch == '!' || ch == '?') {
                inSentence = false;
                inWord = false;
            } else if (ch == ' ') {
                inWord = false;
            } else {
                // Start of a new word.
                if (!inWord && Character.isLetter(ch)) {
                    inWord = true;
                    wordCount++;
                }

                // Start of a new sentence.
                if (!inSentence) {
                    inSentence = true;
                    sentenceCount++;
                }
            }
        }

        ArrayList<Integer> res = new ArrayList<>();
        res.add(sentenceCount);
        res.add(wordCount);

        return res;
    }

    public static void main(String[] args) {
        String s = "Sentences";
        System.out.println(sentenceWord(s));

        s = "many??? Sentences are";
        System.out.println(sentenceWord(s));
    }
}

def sentenceWord(s):
    sentenceCount = 0
    wordCount = 0

    inSentence = False
    inWord = False

    for ch in s:
        if ch == '.' or ch == '!' or ch == '?':
            inSentence = False
            inWord = False
        elif ch == ' ':
            inWord = False
        else:
            # Start of a new word.
            if not inWord and ch.isalpha():
                inWord = True
                wordCount += 1

            # Start of a new sentence.
            if not inSentence:
                inSentence = True
                sentenceCount += 1

    return [sentenceCount, wordCount]


if __name__ == "__main__":
    s = "Sentences"
    print(sentenceWord(s))

    s = "many??? Sentences are"
    print(sentenceWord(s))

using System;
using System.Collections.Generic;

public class GFG
{
    static List<int> sentenceWord(string s)
    {
        int sentenceCount = 0;
        int wordCount = 0;

        bool inSentence = false;
        bool inWord = false;

        foreach (char ch in s)
        {
            if (ch == '.' || ch == '!' || ch == '?')
            {
                inSentence = false;
                inWord = false;
            }
            else if (ch == ' ')
            {
                inWord = false;
            }
            else
            {
                // Start of a new word.
                if (!inWord && char.IsLetter(ch))
                {
                    inWord = true;
                    wordCount++;
                }

                // Start of a new sentence.
                if (!inSentence)
                {
                    inSentence = true;
                    sentenceCount++;
                }
            }
        }

        return new List<int> { sentenceCount, wordCount };
    }

    public static void Main()
    {
        string s = "Sentences";
        List<int> res = sentenceWord(s);
        Console.WriteLine("[" + string.Join(", ", res) + "]");

        s = "many??? Sentences are";
        res = sentenceWord(s);
        Console.WriteLine("[" + string.Join(", ", res) + "]");
    }
}

/**
 * @param {string} s
 * @returns {number[]}
 */
function sentenceWord(s) {
    let sentenceCount = 0;
    let wordCount = 0;

    let inSentence = false;
    let inWord = false;

    for (const ch of s) {
        if (ch === '.' || ch === '!' || ch === '?') {
            inSentence = false;
            inWord = false;
        } else if (ch === ' ') {
            inWord = false;
        } else {
            // Start of a new word.
            if (!inWord && /[a-zA-Z]/.test(ch)) {
                inWord = true;
                wordCount++;
            }

            // Start of a new sentence.
            if (!inSentence) {
                inSentence = true;
                sentenceCount++;
            }
        }
    }

    return [sentenceCount, wordCount];
}

// Driver Code
let s = "Sentences";
let res = sentenceWord(s);
console.log("[" + res.join(", ") + "]");

s = "many??? Sentences are";
res = sentenceWord(s);
console.log("[" + res.join(", ") + "]");

[1, 1]
[2, 3]