Add Pascal's triangle in JavaScript

algorithms/JavaScript/src/dynamic-programming/pascals-triangle.js

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+/*
+
+Problem -
+
+    Given an integer (numRows), return the first numRows of Pascal's triangle.
+
+    Pascal's triangle - each number is the sum of the two numbers directly above it 
+
+Example -
+
+    Input: n = 5
+
+    Output: [[1], [1, 1], [1, 2, 1], [1, 3, 3, 1], [1, 4, 6, 4, 1]]
+
+    Visualization:
+        1
+       1 1
+      1 2 1
+     1 3 3 1
+    1 4 6 4 1
+
+Time Complexity - O(n^2) n = number of rows
+
+Space Complexity - O(1) excluding the result array
+
+*/
+
+init();
+
+function getPascalsTriangle(numRows) {
+
+    // Base case: the tip of Pascal's triangle always starts with 1
+    const pasTri = [[1]];
+    
+    // Start looping through the next row of Pascal's triangle until we reach the end
+    for(let i = 1; i < numRows; i++) {
+
+        // Initialize the next row of Pascal's triangle
+        const nextRow = [];
+        
+        // Builds the next row of Pascal's triangle
+        for(let j = 0; j <= i; j++) {
+
+            // Gets the upper left and right values from the previous row
+            // If the upper left or right values doesn't exist, use 0 instead
+            const firstVal = pasTri[i - 1][j - 1] || 0;
+            const secVal = pasTri[i - 1][j] || 0;
+
+            // Push the new combined value to the current row of Pascal's triangle
+            nextRow.push(firstVal + secVal);
+        }
+
+        // Add the next row to our original Pascal's triangle
+        pasTri.push(nextRow);
+    }
+    
+    return pasTri;
+}
+
+function testPascalsTriangle(numRows) {
+    const pascalTriangle = getPascalsTriangle(numRows);
+
+    console.log("Number of rows: ", numRows);
+
+    printTriangle(pascalTriangle);
+
+    console.log("Test complete!");
+}
+
+function printTriangle(pascalTriangle) {
+    const SPACE = " ";
+
+    for (let row = 0; row < pascalTriangle.length; row++) {
+        const leadingSpace = SPACE.repeat(pascalTriangle.length - row - 1);
+        const currentRowInTriangle = pascalTriangle[row].join(SPACE);
+
+        console.log(leadingSpace + currentRowInTriangle);
+    }
+}
+
+function init() {
+    const readline = require('readline').createInterface({
+        input: process.stdin,
+        output: process.stdout
+    });
+
+    readline.question('Please enter the number of rows to print\n', numRows => {
+        if (numRows >= 1) {
+            testPascalsTriangle(numRows);
+        } else {
+            console.log("Please enter a valid number!");
+        }
+
+        readline.close();
+    });
+}