Permuted multiples
- Attribution
The following task is taken from Project Euler.
- Task
Find the smallest positive integer n such that, when expressed in decimal, 2*n, 3*n, 4*n, 5*n, and 6*n contain exactly the same digits but in a different order.
Go
<lang go>package main
import (
"fmt" "rcu" "sort"
)
// assumes l1 is sorted but l2 is not func areSame(l1, l2 []int) bool {
if len(l1) != len(l2) {
return false
}
sort.Ints(l2)
for i := 0; i < len(l1); i++ {
if l1[i] != l2[i] {
return false
}
}
return true
}
func main() {
i := 100 // clearly a 1 or 2 digit number is impossible
nextPow := 1000
for {
digits := rcu.Digits(i, 10)
if digits[0] != 1 {
i = nextPow
nextPow *= 10
continue
}
sort.Ints(digits)
allSame := true
for j := 2; j <= 6; j++ {
digits2 := rcu.Digits(i*j, 10)
if !areSame(digits, digits2) {
allSame = false
break
}
}
if allSame {
fmt.Println("The smallest positive integer n for which the following")
fmt.Println("multiples contain exactly the same digits is:")
fmt.Println(" n =", i)
for k := 2; k <= 6; k++ {
fmt.Printf("%d x n = %d\n", k, k*i)
}
return
}
i = i + 1
}
}</lang>
- Output:
The smallest positive integer n for which the following
multiples contain exactly the same digits is:
n = 142857
2 x n = 285714
3 x n = 428571
4 x n = 571428
5 x n = 714285
6 x n = 857142
Phix
Maintain a limit (n10) and bump the iteration whenever *6 increases the number of digits, which (as shown) cuts the number of iterations by a factor of nearly thirteen and a half times (as in eg 67 iterations instead of 900 to find nothing in 100..1,000).
with javascript_semantics integer n = 1, n10 = 10 while true do if n*6>=n10 then printf(1,"Nothing less than %,d (%,d)\n",{n10,n}) n = n10 n10 *= 10 else string ns = sort(sprintf("%d",n)) integer i -- (for test after loop) for i=2 to 6 do string ins = sort(sprintf("%d",n*i)) if ins!=ns then exit end if end for if i=7 then exit end if n += 1 end if end while constant fmt=""" Smallest positive integer n for which (1..6)*n contain the same digits: n = %d 2 x n = %d 3 x n = %d 4 x n = %d 5 x n = %d 6 x n = %d """ printf(1,fmt,sq_mul(n,tagset(6)))
- Output:
Nothing less than 10 (2)
Nothing less than 100 (17)
Nothing less than 1,000 (167)
Nothing less than 10,000 (1,667)
Nothing less than 100,000 (16,667)
Smallest positive integer n for which (1..6)*n contain the same digits:
n = 142857
2 x n = 285714
3 x n = 428571
4 x n = 571428
5 x n = 714285
6 x n = 857142
Raku
<lang perl6>put display (^∞).map(1 ~ *).race.map( -> \n { next unless [eq] (2,3,4,5,6).map: { (n × $_).comb.sort.join }; n } ).first;
sub display ($n) { join "\n", " n: $n", (2..6).map: { "×$_: {$n×$_}" } }</lang>
- Output:
n: 142857 ×2: 285714 ×3: 428571 ×4: 571428 ×5: 714285 ×6: 857142
REXX
<lang rexx>/*REXX program finds and displays the smallest positive integer n such that ··· */ /*───────────────────────── 2*n, 3*n, 4*5, 5*6, and 6*n contain the same decimal digits.*/
do n=1 /*increment N from unity. */
b= 2*n /*calculate product of 2*n*/
t= 3*n /* " " " 3*n*/
if verify(t,b)>0 then iterate /*product have req. digs ?*/
q= 4*n /*calculate product of 4*n*/
if verify(q,b)>0 then iterate /*product have req. digs ?*/
if verify(q,t)>0 then iterate /* " " " " "*/
v= 5*n /*calculate product of 5*n*/
if verify(v,b)<0 then iterate /*product have req. digs ?*/
if verify(v,t)>0 then iteratr /* " " " " "*/
if verify(v,q)>0 then iteratr /* " " " " "*/
s= 6*n /*calculate product of 6*n*/
if verify(s,b)>0 then iterate /*product have req. digs ?*/
if verify(s,t)>0 then iterate /* " " " " "*/
if verify(s,q)>0 then iterate /* " " " " "*/
if verify(s,v)>0 then iterate /* " " " " "*/
leave /*found the numbers, show.*/
end /*n*/
_= left(, 9) /*used for indentation. */ say _ ' n =' commas(n) /*display value of n. */ say _ '2*n =' commas(b) /* " " " 2*n. */ say _ '3*n =' commas(t) /* " " " 3*n. */ say _ '4*n =' commas(q) /* " " " 4*n. */ say _ '5*n =' commas(v) /* " " " 5*n. */ say _ '6*n =' commas(s) /* " " " 6*n. */ exit 0 /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ commas: parse arg ?; do jc=length(?)-3 to 1 by -3; ?=insert(',', ?, jc); end; return ?</lang>
- output when using the internal default input:
n = 142,857
2*n = 285,714
3*n = 428,571
4*n = 571,428
5*n = 714,285
6*n = 857,142
Ring
<lang ring> load "stdlib.ring"
see "working..." + nl see "Permuted multiples are:" + nl per = list(6) perm = list(6)
for n = 1 to 1000000
for x = 2 to 6
perm[x] = []
next
perStr = list(6)
for z = 2 to 6
per[z] = n*z
perStr[z] = string(per[z])
for m = 1 to len(perStr[z])
add(perm[z],perStr[z][m])
next
next
for y = 2 to 6
perm[y] = sort(perm[y])
perStr[y] = list2str(perm[y])
perStr[y] = substr(perStr[y],nl,"")
next
if perStr[2] = perStr[3] and perStr[2] = perStr[4] and perStr[2] = perStr[5] and perStr[2] = perStr[6]
see "n = " + n + nl
see "2*n = " + (n*2) + nl
see "3*n = " + (n*3) + nl
see "4*n = " + (n*4) + nl
see "5*n = " + (n*5) + nl
see "6*n = " + (n*6) + nl
exit
ok
next
see "done..." + nl </lang>
- Output:
working... Permuted multiples are: n = 142857 2*n = 285714 3*n = 428571 4*n = 571428 5*n = 714285 6*n = 857142 done...
Wren
One thing that's immediately clear is that the number must begin with '1' otherwise the higher multiples will have more digits than it has. <lang ecmascript>import "/math" for Int
// assumes l1 is sorted but l2 is not var areSame = Fn.new { |l1, l2|
if (l1.count != l2.count) return false
l2.sort()
for (i in 0...l1.count) {
if (l1[i] != l2[i]) return false
}
return true
}
var i = 100 // clearly a 1 or 2 digit number is impossible var nextPow = 1000 while (true) {
var digits = Int.digits(i)
if (digits[0] != 1) {
i = nextPow
nextPow = nextPow * 10
continue
}
digits.sort()
var allSame = true
for (j in 2..6) {
var digits2 = Int.digits(i * j)
if (!areSame.call(digits, digits2)) {
allSame = false
break
}
}
if (allSame) {
System.print("The smallest positive integer n for which the following")
System.print("multiples contain exactly the same digits is:")
System.print(" n = %(i)")
for (k in 2..6) System.print("%(k) x n = %(k * i)")
return
}
i = i + 1
}</lang>
- Output:
The smallest positive integer n for which the following
multiples contain exactly the same digits is:
n = 142857
2 x n = 285714
3 x n = 428571
4 x n = 571428
5 x n = 714285
6 x n = 857142