LeetCode's Pascal's Triangle

Given an integer numRows, return the first numRows of Pascal's triangle.
In Pascal's triangle, each number is the sum of the two numbers directly
above it.

javascript/pascalTriangle.js

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+/**
+ * Visit https://leetcode.com/problems/pascals-triangle/description/
+ * for full problem description
+ * 
+ * Given an integer numRows, return the first numRows of Pascal's triangle.
+ * In Pascal's triangle, each number is the sum of the two numbers directly above it
+ * 
+ * @param {number} numRows
+ * @return {number[][]}
+ */
+var generate = function (numRows) {
+    if (numRows === 1) {
+        return [[1]];
+    }
+
+    let pascalTriangle = [[1]]
+    for (let i = 1; i < numRows; i++) {
+        // Each element in the triangle is an array
+        pascalTriangle[i] = [];
+        lengthOfPrevArray = i; // pascalTriangle[i - 1].length
+        for (let j = 0; j <= lengthOfPrevArray; j++) {
+            // The first and last numbers in any row (array) of the triangle are 1s
+            if (j === 0 || j == lengthOfPrevArray) {
+                pascalTriangle[i][j] = 1;
+            } else {
+                // Other numbers in the row (array) are the sums of the two numbers directly above it
+                // i.e the sums of the numbers in the previous array at the same position, j, plus 
+                // the previous position, j - 1
+                pascalTriangle[i][j] =
+                    pascalTriangle[i - 1][j - 1] + pascalTriangle[i - 1][j];
+            }
+        }
+    }
+
+    return pascalTriangle;
+
+
+
+};