CodingGyan

Word Prefix Triangle

beginner Pattern Printing

Problem

Read one word and print its prefixes, one on each line. Row 1 has the first letter, row 2 has the first two letters, and the last row is the whole word. Example: india gives i, in, ind, indi, india.

Constraints

  • 1 <= length of word <= 100
  • The word has no spaces

Examples

Input

india

Output

i
in
ind
indi
india

Solutions

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

A prefix is the beginning of a word. The substring (slice) of the first k letters is the prefix of length k, so one loop from 1 to the word length is enough.

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 : Prefixes of a word.
 * Input   : One word without spaces.
 * Output  : One line for each prefix.
 * Approach: Take a part of the word that grows by one letter.
 * Time    : O(n^2)
 * Space   : O(n)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

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

        // Step 1: Repeat once for each letter. "length" is the size of the prefix.
        for (int length = 1; length <= word.length(); length++) {
            // Step 2: Take the first "length" letters. substring(0, 3) of "india" is "ind".
            String prefix = word.substring(0, length);

            // Step 3: Print the prefix.
            System.out.println(prefix);
        }
    }
}
Hints (2)
  1. How do you take the first k letters of a string?
  2. The end index of substring is not included.

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