Ludic numbers: Difference between revisions
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Line 4,614:
221, 223, 227
233, 235, 239
</pre>
=={{header|Vlang}}==
{{trans|Go}}
<lang vlang>const max_i32 = 1<<31 - 1 // i.e. math.MaxInt32
// ludic returns a slice of ludic numbers stopping after
// either n entries or when max is exceeded.
// Either argument may be <=0 to disable that limit.
fn ludic(nn int, m int) []u32 {
mut n := nn
mut max := m
if max > 0 && n < 0 {
n = max_i32
}
if n < 1 {
return []
}
if max < 0 {
max = max_i32
}
mut sieve := []u32{len: 10760} // XXX big enough for 2005 ludics
sieve[0] = 1
sieve[1] = 2
if n > 2 {
// We start with even numbers already removed
for i, j := 2, u32(3); i < sieve.len; i, j = i+1, j+2 {
sieve[i] = j
}
// We leave the ludic numbers in place,
// k is the index of the next ludic
for k := 2; k < n; k++ {
mut l := int(sieve[k])
if l >= max {
n = k
break
}
mut i := l
l--
// last is the last valid index
mut last := k + i - 1
for j := k + i + 1; j < sieve.len; i, j = i+1, j+1 {
last = k + i
sieve[last] = sieve[j]
if i%l == 0 {
j++
}
}
// Truncate down to only the valid entries
if last < sieve.len-1 {
sieve = sieve[..last+1]
}
}
}
if n > sieve.len {
panic("program error") // should never happen
}
return sieve[..n]
}
fn has(x []u32, v u32) bool {
for i := 0; i < x.len && x[i] <= v; i++ {
if x[i] == v {
return true
}
}
return false
}
fn main() {
// ludic() is so quick we just call it repeatedly
println("First 25: ${ludic(25, -1)}")
println("Numner of ludics below 1000: ${ludic(-1, 1000).len}")
println("ludic 2000 to 2005: ${ludic(2005, -1)[1999..]}")
print("Tripples below 250:")
x := ludic(-1, 250)
for i, v in x[..x.len-2] {
if has(x[i+1..], v+2) && has(x[i+2..], v+6) {
print(", ($v ${v+2} ${v+6})")
}
}
println('')
}</lang>
{{out}}
<pre>
First 25: [1, 2, 3, 5, 7, 11, 13, 17, 23, 25, 29, 37, 41, 43, 47, 53, 61, 67, 71, 77, 83, 89, 91, 97, 107]
Numner of ludics below 1000: 142
ludic 2000 to 2005: [21475, 21481, 21487, 21493, 21503, 21511]
Tripples below 250:, (1 3 7), (5 7 11), (11 13 17), (23 25 29), (41 43 47), (173 175 179), (221 223 227), (233 235 239)
</pre>
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