Is Pascal's Triangle easy or hard?

Pascal's Triangle is considered an easy problem on most coding platforms. The challenge is recognizing the relationship between adjacent rows and implementing the row-by-row construction correctly using arrays.

How to solve Pascal's Triangle in O(n)?

Producing the full triangle cannot be done in O(n) because the output itself contains O(n^2) numbers. However, generating a single row can be done in O(n) time using combinatorial formulas or incremental updates based on binomial coefficients.

What is the best approach for Pascal's Triangle?

The iterative construction approach using dynamic programming is the most practical solution. Build the triangle row by row and compute each inner value as the sum of the two numbers above it. This method runs in O(n^2) time and uses O(n^2) space to store the triangle, which is optimal since all elements must be generated.

What data structure is used in Pascal's Triangle?

The typical implementation uses a 2D array or a list of lists to store rows of the triangle. Each row is built using values from the previous row, which makes it a simple dynamic programming problem built on top of array indexing.

What is the time complexity of Pascal's Triangle?

Generating the first n rows requires computing n(n+1)/2 elements. Every element is calculated once, so the time complexity is O(n^2). Both iterative and recursive approaches share the same complexity because they must construct the entire triangle.

Pascal's Triangle Python or Java solution approach?

Both Python and Java implementations follow the same idea: iterate from row 0 to numRows-1, initialize each row with 1s at the edges, and compute middle values using the previous row. The algorithm runs in O(n^2) time and stores the result in a list of arrays or lists.

Is Pascal's Triangle asked at Google, Amazon, or Meta interviews?

Pascal's Triangle appears frequently in coding interviews at large tech companies and is common in early interview rounds. It tests array manipulation, understanding of recurrence relations, and basic dynamic programming concepts rather than advanced algorithms.

Description Solution Video 9:20

118. Pascal's Triangle

Easy79.4% acceptance17 companies

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 as shown:

Example 1:

Input: numRows = 5
Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Example 2:

Input: numRows = 1
Output: [[1]]

Constraints:

1 <= numRows <= 30

Asked at 17 companies

Twitter Htc Bank of America Deutsche Bank Mitsogo

Google Amazon Microsoft Bloomberg Apple Accenture Wipro

+5 more

Meta Goldman Sachs

TCS Zoho JPMorgan Chase

Topics

Array Dynamic Programming

9:20

Still stuck?Read 3 approaches, or watch a walkthrough.

Open solution

118. Pascal's Triangle

Asked at 17 companies

Topics

Similar problems