Lesson guide
What this Python exercise practices
Generate Pascal's Triangle is a advanced practice lesson that focuses on dsa, problem patterns, edge cases. It is designed to be solved in about 24 minutes with examples, starter code, and test feedback.
Prerequisites
- Python functions
- Loops
- Lists
- Basic edge cases
Difficulty and time
- Level
- Advanced
- Estimated time
- 24 minutes
Practice path
Summary
Produce the first n rows of Pascal's triangle using loops.
Problem statement
Write pascals_triangle(n) that returns a list of lists representing the first n rows (top to bottom) of Pascal's triangle. Each row is a list of integers. Rules: - Row 1 is [1]. - Each element inside a row (not on edges) is the sum of the two elements above it from the previous row. - If n is 0, return an empty list. Use loops to build rows iteratively. Aim for clarity and correctness for n up to at least 20.
Task
Implement a function to generate Pascal's triangle rows iteratively without using recursion or external libraries.
Examples
First 5 rows
Input
pascals_triangle(5)
Output
[[1], [1, 1], [1, 2, 1], [1, 3, 3, 1], [1, 4, 6, 4, 1]]
Explanation
Each row is built from the previous row by summing adjacent pairs and adding 1s at the ends.
Input format
A single integer n (number of rows).
Output format
A list of n lists, each inner list is a row of integers from Pascal's triangle.
Constraints
0 <= n <= 20. Time complexity O(n^2) is acceptable. Use loops (for/while) to build the triangle.
Samples
Sample input 0
pascals_triangle(3)
Sample output 0
[[1], [1, 1], [1, 2, 1]]
Explanation 0
Three rows starting from [1].
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