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"""

Print all the Catalan numbers from 0 to n, n being the user input.

* The Catalan numbers are a sequence of positive integers that

* appear in many counting problems in combinatorics [1]. Such

* problems include counting [2]:

* - The number of Dyck words of length 2n

* - The number well-formed expressions with n pairs of parentheses

* (e.g., `()()` is valid but `())(` is not)

* - The number of different ways n + 1 factors can be completely

* parenthesized (e.g., for n = 2, C(n) = 2 and (ab)c and a(bc)

* are the two valid ways to parenthesize.

* - The number of full binary trees with n + 1 leaves

* A Catalan number satisfies the following recurrence relation

* which we will use in this algorithm [1].

* C(0) = C(1) = 1

* C(n) = sum(C(i).C(n-i-1)), from i = 0 to n-1

* In addition, the n-th Catalan number can be calculated using

* the closed form formula below [1]:

* C(n) = (1 / (n + 1)) * (2n choose n)

* Sources:

* [1] https://brilliant.org/wiki/catalan-numbers/

* [2] https://en.wikipedia.org/wiki/Catalan_number

"""

def catalan_numbers(upper_limit: int) -> "list[int]":

"""

Return a list of the Catalan number sequence from 0 through `upper_limit`.

>>> catalan_numbers(5)

[1, 1, 2, 5, 14, 42]

>>> catalan_numbers(2)

[1, 1, 2]

>>> catalan_numbers(-1)

Traceback (most recent call last):

ValueError: Limit for the Catalan sequence must be ≥ 0

"""

if upper_limit < 0:

raise ValueError("Limit for the Catalan sequence must be ≥ 0")

catalan_list = [0] * (upper_limit + 1)

# Base case: C(0) = C(1) = 1

catalan_list[0] = 1

if upper_limit > 0:

catalan_list[1] = 1

# Recurrence relation: C(i) = sum(C(j).C(i-j-1)), from j = 0 to i

for i in range(2, upper_limit + 1):

for j in range(i):

catalan_list[i] += catalan_list[j] * catalan_list[i - j - 1]

return catalan_list

if __name__ == "__main__":

print("\n********* Catalan Numbers Using Dynamic Programming ************\n")

print("\n*** Enter -1 at any time to quit ***")

print("\nEnter the upper limit (≥ 0) for the Catalan number sequence: ", end="")

try:

while True:

N = int(input().strip())

if N < 0:

print("\n********* Goodbye!! ************")

break

else:

print(f"The Catalan numbers from 0 through {N} are:")

print(catalan_numbers(N))

print("Try another upper limit for the sequence: ", end="")

except (NameError, ValueError):

print("\n********* Invalid input, goodbye! ************\n")

import doctest

doctest.testmod()

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