Advanced String Manipulation Question

You are given a string sentence and a string word, both containing only lowercase alphabetical characters. You need to implement a function countOccurrences(sentence: str, word: str) -> int that counts the number of occurrences of the word in the sentence, considering both exact matches and matches that differ by a single character.

Additionally, you should consider only the occurrences of the word that are in the same order as the characters in the word. For example, if word is "abc" and sentence is "abbcac", the only valid occurrence would be "abbc" because it follows the order of characters in "abc".

Please write the function countOccurrences and provide step-by-step explanation.

public class StringManipulation {
    
    public static int countOccurrences(String sentence, String word) {
        int count = 0;
        int wordPointer = 0;
        
        for (int i = 0; i < sentence.length(); i++) {
            if (sentence.charAt(i) == word.charAt(wordPointer)) {
                wordPointer++;
                
                if (wordPointer == word.length()) {
                    count++;
                    wordPointer = 0;
                }
            } else {
                wordPointer = 0;

                if (sentence.charAt(i) == word.charAt(0))
                    wordPointer = 1;
            }
        }
        
        return count;
    }
    
    public static void main(String[] args) {
        String sentence = "abbcbac";
        String word = "abc";
        
        int occurrences = countOccurrences(sentence, word);
        System.out.println("Occurrences: " + occurrences);
    }
}

Step-by-Step Explanation:

1. Start by declaring the count variable to keep track of the number occurrences of the word.
2. Initialize the wordPointer variable to keep track of the index within the word string.
3. Iterate over each character of the sentence string using a for loop.
4. Check if the current character matches the character at the corresponding position within the word string using sentence.charAt(i) == word.charAt(wordPointer).
   • If the characters match, increment the wordPointer by 1.
   • If wordPointer becomes equal to the length of word, it means a full occurrence of word is found in sentence. Increment the count by 1 and reset wordPointer to 0.
5. If the characters do not match, reset wordPointer to 0.
   • But before resetting, check if the current character matches the first character of word using sentence.charAt(i) == word.charAt(0).
   • If they match, set wordPointer to 1 to start checking the next character in the next iteration, since it could potentially be a partial match.
6. After iterating over all characters in the sentence, return the final count.

In the given question, the main function demonstrates how to use the countOccurrences function. It initializes the sentence and word variables, then calls the countOccurrences function passing these variables and stores the result in the occurrences variable. Finally, it prints the value of occurrences to the console.