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tommy-3

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Learning Algorithms with JS, Python and Java #10: Pyramid

This series of articles follows Stephen Grider's Udemy course in three different languages.

Today's question is a slight variation on the last one.

--- Directions
Write a function that accepts a positive number N.
The function should console log a pyramid shape
with N levels using the # character. Make sure the
pyramid has spaces on both the left and right hand sides
--- Examples
pyramid(1)
'#'
pyramid(2)
' # '
'###'
pyramid(3)
' # '
' ### '
'#####'

1: Iterative Solution

JavaScript:

function pyramid(n) {
    const columnCount = 2 * n - 1;
    const midColumn = Math.floor(columnCount / 2);

    for (let row = 0; row < n; row++) {
        let level = '';

        for (let column = 0; column < columnCount; column++) {
            if (Math.abs(column - midColumn) <= row) {
                level += '#';
            } else {
                level += ' ';
            }
        }

        console.log(level);
    }
}

Python:

def pyramid(n):
    column_count = 2 * n - 1
    mid_column = column_count // 2

    for row in range(n):
        level = ''

        for column in range(column_count):
            if abs(column - mid_column) <= row:
                level += '#'
            else:
                level += ' '

        print(level)

Java:

static void pyramid1(int n) {
    int columnCount = 2 * n - 1;
    int midColumn = columnCount / 2;

    for (int row = 0; row < n; row++) {
        StringBuilder level = new StringBuilder();

        for (int column = 0; column < columnCount; column++) {
            if (Math.abs(column - midColumn) <= row) {
                level.append("#");
            } else {
                level.append(" ");
            }
        }

        System.out.println(level);
    }
}

2: Recursive Solution

Here I take an approach a bit different from the one introduced in the course.

JavaScript:

function pyramid(n, row = 0, level = '#') {
    if (n === row) {
        return;
    }

    if (level.length === 2 * n - 1) {
        console.log(level);
        return pyramid(n, row + 1);
    }

    level = level.length < 2 * row ? `#${level}#` : ` ${level} `;
    pyramid(n, row, level);
}

Python:

def pyramid(n, row=0, level='#'):
    if n == row:
        return

    if len(level) == 2 * n - 1:
        print(level)
        return pyramid(n, row+1)

    level = f'#{level}#' if len(level) < 2 * row else f' {level} '
    pyramid(n, row, level)

Java:

static void pyramid(int n) {
    pyramid(n, 0, new StringBuilder("#"));
}

static void pyramid(int n, int row, StringBuilder level) {
    if (n == row) {
        return;
    }

    if (level.length() == 2 * n - 1) {
        System.out.println(level);
        pyramid(n, row + 1, new StringBuilder("#"));
        return;
    }

    if (level.length() < 2 * row) {
        level.insert(0, "#").append("#");
    } else {
        level.insert(0, " ").append(" ");
    }

    pyramid(n, row, level);
}

Thank you for reading. I do plan to write this series more often, so I hope to see you soon!

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