Problema
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}
};Explicación
The 2 in row 3 is 1 + 1. The two interior 3s in row 4 are 1 + 2 and 2 + 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[][] {};Explicación
No rows are requested, so return an empty list.
Cómo abordarlo
Inténtalo primero por tu cuenta y luego abre las pistas una a una.
Pista 1
Each row starts and ends with 1, and interior values come from the two values above them.
Pista 2
Build rows one at a time from the previous row rather than recomputing from scratch.
Pista 3
Handle the zero-row case by returning an empty list immediately.
Complejidad esperada
O(rows^2) time, O(rows^2) extra space
Referencias
Este reto está adaptado para CodeUtility. Sigue el enunciado y las restricciones indicadas arriba.