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Print Character Triangle in Java

beginner· Patterns · Character Patterns

Problem

Since a char is really just a small integer under the hood, adding an offset to 'A' walks through the alphabet the same way adding to a loop counter walks through numbers.

Given a number of rows, print a left-aligned triangle where row i contains the first i letters of the alphabet.

Input

5

Output

A
A B
A B C
A B C D
A B C D E

Java Program

Java

public class CharacterTriangle {
    public static void main(String[] args) {
        int n = 5;

        for (int i = 1; i <= n; i++) {
            StringBuilder row = new StringBuilder();
            for (int j = 0; j < i; j++) {
                if (j > 0) row.append(" ");
                row.append((char) ('A' + j)); // 'A' + j walks forward through the alphabet
            }
            System.out.println(row);
        }
    }
}

▶ Run Code

Output

A
A B
A B C
A B C D
A B C D E

Core Logic

Casting an integer offset onto the letter 'A' turns the same row-and-column counting used for a star triangle into a sequence of letters instead.

How It Works

1The outer loop runs i from 1 to n, one pass per row.
2The inner loop runs j from 0 to i - 1, one pass per letter in that row.
3(char) ('A' + j) converts the column index directly into the matching letter, since char values are just numeric codes underneath.
4Each row's letters are joined with single spaces and printed once the inner loop finishes.

For row 4, j runs 0 through 3, producing 'A'+0, 'A'+1, 'A'+2, 'A'+3 — the letters A B C D.

💡

Key Point: The inner loop never needs to know it's building letters instead of numbers — only the single line that converts j into a character changes from a numeric pattern.

Complexity

Time Complexity: O(n²)Space Complexity: O(1)

Why: The total letters printed across every row grows proportionally to n², and only the loop counters and a per-row StringBuilder are kept at any point.

Key Concepts

nested for loopchar arithmeticStringBuilder

Approach 2: Java 8

Java

import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class CharacterTriangleStream {
    public static void main(String[] args) {
        int n = 5;
        IntStream.rangeClosed(1, n)
            .mapToObj(i -> IntStream.range(0, i)
                .mapToObj(j -> String.valueOf((char) ('A' + j)))
                .collect(Collectors.joining(" ")))
            .forEach(System.out::println);
    }
}

▶ Run Code

Output

A
A B
A B C
A B C D
A B C D E

Core Logic

The same row-by-row letter sequence can be produced by mapping each row's column indices directly to their letters and joining the results.

How It Works

1IntStream.rangeClosed(1, n) generates one stream element per row.
2For each row i, an inner IntStream.range(0, i) generates that row's column indices.
3.mapToObj(j -> String.valueOf((char) ('A' + j))) converts each column index into its letter.
4Collectors.joining(" ") joins that row's letters with spaces before forEach prints it.

For row 4, the inner stream maps 0, 1, 2, 3 to A, B, C, D and joins them into "A B C D".

💡

Key Point: Nesting one stream inside another mirrors the nested loop exactly — the outer stream picks the row, the inner stream builds that row's content.

Complexity

Time Complexity: O(n²)Space Complexity: O(1)

Why: The nested streams still visit every letter position across every row exactly once, without collecting the full triangle into a stored structure.

Print Character Triangle in Java

Problem

Java Program

Output

Core Logic

Key Concepts

Approach 2: Java 8

Output

Core Logic

Key Concepts

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