Given a sentence delimited by spaces, reverse the sentence.

ReverseWords.java

public String reverseWords(String s) {
    String[] a = s.replaceAll("\\s+", " ").split(" ");
    int i = 0, j = a.length-1;
    while(i < j) {
        String temp = a[i];
        a[i++] = a[j];
        a[j--] = temp;
    }

    return String.join(" ", a).trim();
}