Pascal's Triangle

pascal-triangle.js

'use strict';

/**
 * Display a Pascal Triangle
 *
 * @param {number} numRows Number of rows to display
 */
const displayPascalTriangle = function (numRows = 0) {

  if (numRows < 0) {
    console.log('Error: numRows must not be negative');
  }

  const triangle = [];

  // Rows
  for (let n = 0; n < numRows; n++) {

    triangle[n] = [];

    // Cols
    for (let k = 0; k <= n; k++) {

      if (k === 0 || k === n) {

        // First and last numbers in row are always 1
        triangle[n][k] = 1;
      }
      else {

        // Inside numbers are the sum of the 2 numbers directly "above" them
        triangle[n][k] = triangle[n-1][k-1] + triangle[n-1][k];
      }
    }

    // Display row (left justified)
    console.log(triangle[n].join(' '));
  }
};