Bell numbers: Difference between revisions

=={{header|Kotlin}}==

{{trans|C}}

<lang scala>class BellTriangle(n: Int) {

private val arr: Array<Int>

init {

val length = n * (n + 1) / 2

arr = Array(length) { 0 }

set(1, 0, 1)

for (i in 2..n) {

set(i, 0, get(i - 1, i - 2))

for (j in 1 until i) {

val value = get(i, j - 1) + get(i - 1, j - 1)

set(i, j, value)

}

}

}

private fun index(row: Int, col: Int): Int {

require(row > 0)

require(col >= 0)

require(col < row)

return row * (row - 1) / 2 + col

}

operator fun get(row: Int, col: Int): Int {

val i = index(row, col)

return arr[i]

}

private operator fun set(row: Int, col: Int, value: Int) {

val i = index(row, col)

arr[i] = value

}

}

fun main() {

val rows = 15

val bt = BellTriangle(rows)

println("First fifteen Bell numbers:")

for (i in 1..rows) {

println("%2d: %d".format(i, bt[i, 0]))

}

for (i in 1..10) {

print("${bt[i, 0]}")

for (j in 1 until i) {

print(", ${bt[i, j]}")

}

println()

}

}</lang>

{{out}}

<pre>First fifteen Bell numbers:

1: 1

2: 1

3: 2

4: 5

5: 15

6: 52

7: 203

8: 877

9: 4140

10: 21147

11: 115975

12: 678570

13: 4213597

14: 27644437

15: 190899322

1

1, 2

2, 3, 5

5, 7, 10, 15

15, 20, 27, 37, 52

52, 67, 87, 114, 151, 203

203, 255, 322, 409, 523, 674, 877

877, 1080, 1335, 1657, 2066, 2589, 3263, 4140

4140, 5017, 6097, 7432, 9089, 11155, 13744, 17007, 21147

21147, 25287, 30304, 36401, 43833, 52922, 64077, 77821, 94828, 115975</pre>