Generates a row of Pascal's Triangle (zero-indexed).

pascals-triangle.js

'use strict';

module.exports = {
    getRow: getRow
};

/**
 * Generates a row of Pascal's Triangle, given row number n (zero-indexed).
 * @param   {Number} n
 * @returns {Array<Number>}
 */
function getRow(n) {
    var row = [1];
    var numerator = n;
    var x = 1;
    var l = Math.floor((n / 2) + 1);
    var i;

    // Fill first half of array.
    for (i = 1; i < l; i++, numerator--) {
        x = Math.round((x * numerator) / i);
        row.push(x);
    }

    // Depending on if n is even or odd will determine whether or not we need
    // to read from one space back in row, or two.
    x = n % 2 === 1 ? i - 1 : i - 2;

    // Fill second half of array.
    for (; i <= n; i++, x--) {
        row.push(row[x]);
    }

    return row;
}