Look-and-Say Sequence

/*
 * Problem : Print the first n terms of the look-and-say sequence.
 * Input   : One integer n.
 * Output  : n lines, one term per line.
 * Approach: Read the previous term aloud: count equal digits in a row.
 * Time    : O(L) per term
 * Space   : O(L)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method receives one term and returns the next term. Example: "21" -> "1211".
    static String nextTerm(String term) {
        StringBuilder next = new StringBuilder();
        int index = 0;

        // Step 1: Go through the term from left to right.
        while (index < term.length()) {
            // Step 2: Count how many times the same digit repeats in a row. This is called a "run".
            char digit = term.charAt(index);
            int runLength = 0;
            while (index < term.length() && term.charAt(index) == digit) {
                runLength++;
                index++;
            }

            // Step 3: Write the count and then the digit. Example: three 2s -> "32".
            next.append(runLength).append(digit);
        }
        return next.toString();
    }

    public static void main(String[] args) {
        int n = new Scanner(System.in).nextInt();

        // Step 4: Start with the first term "1". Print each term and then calculate the next one.
        String term = "1";
        for (int line = 1; line <= n; line++) {
            System.out.println(term);
            term = nextTerm(term);
        }
    }
}