Pascal’s Triangle

The first row is [1]. Each later row starts and ends with 1. Every interior entry is the sum of the two entries immediately above it. Return the first rows rows, beginning with the single 1.

Implement pascals_triangle(rows).

Input

rows: How many rows to generate.

Output

Return a list of rows, starting at the top; each row is a list of integers.

Restricciones

0 ≤ rows ≤ 60. Every entry fits a signed 64-bit integer. Zero rows returns an empty list.

Ejemplos

Entrada:
rows = 4

Salida esperada:
expected = [
    [1],
    [1, 1],
    [1, 2, 1],
    [1, 3, 3, 1]
]

Entrada:
long long rows = 4;

Salida esperada:
std::vector<std::vector<long long>> expected = {
    {1},
    {1, 1},
    {1, 2, 1},
    {1, 3, 3, 1}
};

Entrada:
long rows = 4;

Salida esperada:
long[][] expected = new long[][] {
    new long[] {1},
    new long[] {1, 1},
    new long[] {1, 2, 1},
    new long[] {1, 3, 3, 1}
};

Entrada:
rows = 0

Salida esperada:
expected = []

Entrada:
long long rows = 0;

Salida esperada:
std::vector<std::vector<long long>> expected = {};

Entrada:
long rows = 0;

Salida esperada:
long[][] expected = new long[][] {};

Referencias

Este reto está adaptado para CodeUtility. Sigue el enunciado y las restricciones indicadas arriba.

• Pascal's Triangle