CodingGyan

Alternating Binary Triangle

easy Pattern Printing

Problem

Read n and print a triangle of 1 and 0 without spaces. Every row starts with 1 and the digits alternate. Row 1 is 1, row 2 is 10, row 3 is 101, and so on.

Constraints

  • 1 <= n <= 30

Examples

Input

3

Output

1
10
101

Solutions

Best approachTime O(n^2)Space O(1)

Each row is the first row digits of the sequence 1010101... The remainder of the position divided by 2 chooses 1 or 0.

Same code works in Java810172125Basic features only, so nothing changes between versions.

Java 8 has no String.repeat, so we use a small helper method. In Java 11 and newer you can write " ".repeat(count).

/*
 * Problem : Alternating digits triangle.
 * Input   : One integer n (rows).
 * Output  : n lines.
 * Approach: Digits at even positions are 1, at odd positions are 0.
 * Time    : O(n^2)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

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

        // Step 1: Repeat once for each row. Row numbers go from 1 to rows.
        for (int row = 1; row <= rows; row++) {
            StringBuilder line = new StringBuilder();

            // Step 2: Write "row" digits. Position 0 is the first digit of the row.
            for (int position = 0; position < row; position++) {
                // Step 3: Even positions (0, 2, 4) give 1. Odd positions (1, 3, 5) give 0.
                line.append(position % 2 == 0 ? "1" : "0");
            }

            // Step 4: Print the finished line.
            System.out.println(line);
        }
    }
}
Hints (2)
  1. Use an outer loop for rows and an inner loop for the letters or digits.
  2. Write the output for n = 3 and look for the rule.

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