def pascal_triangle(n: int):
    if n <= 0:
        return []
    result = []
    row = [1]
    for r in range(1, n+1):
        # r-th row (1-indexed) is 'row'
        result.append(row.copy())
        # build next row
        next_row = [1]
        for i in range(1, len(row)):
            next_row.append(row[i-1] + row[i])
        next_row.append(1)
        row = next_row
    return result
 
# Examples:
# print(pascal_triangle(4)) -> [[1], [1,1], [1,2,1], [1,3,3,1]]
# print(pascal_triangle(5)) -> [[1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1]]
 

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