Longest Common Prefix

/*
 * Problem : Process text.
 * Input   : One line of text.
 * Output  : The common prefix.
 * Approach: Shorten the first word.
 * Time    : O(total characters)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static String solve(String s) {
        // Step 1: Split the line into words. The first word is our first guess for the prefix.
        String[] words = s.trim().split("\\s+");
        String prefix = words[0];

        // Step 2: For each next word, shorten the prefix until the word starts with it.
        for (int i = 1; i < words.length; i++) {
            while (!words[i].startsWith(prefix)) {
                prefix = prefix.substring(0, prefix.length() - 1);
            }
        }

        // Step 3: An empty prefix means there is no common prefix.
        return prefix.isEmpty() ? "none" : prefix;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.hasNextLine() ? scanner.nextLine() : "";
        System.out.println(solve(s));
    }
}