What is the complexity of this simple piece of code?

Question

I\'m pasting this text from an ebook I have. It says the complexity if O(n²) and also gives an explanation for it, but I fail to see how.

Question: What i

Answer 1

I think these text in the book must be a typo ,I think the right content is below,I fix it:

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Question: What is the running time of this code?

public String makeSentence(String[] words) {
    String sentence = new String("");
    for (String w : words) sentence+=W;
    return sentence;
}

Answer: O(n²), where n is the number of letters in sentence. Here’s why: each time you append a string to sentence, you create a copy of sentence and run through all the letters in sentence to copy them over. If you have to iterate through up to n characters each time in the loop, and you’re looping at least n times, that gives you an O(n²) run time. Ouch! With StringBuffer (or StringBuilder) can help you avoid this problem.

public String makeSentence(String[] words) {
    StringBuffer sentence = new StringBuffer();
    for (String w : words) sentence.append(w);
    return sentence.toString();
}

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Am i right?