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320d78a993
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PE3's worked example. Trial-division streaming: when the current
factor divides m, divide and update largest; otherwise bump factor:
let largest_prime_factor n =
let m = ref n in
let factor = ref 2 in
let largest = ref 0 in
while !m > 1 do
if !m mod !factor = 0 then begin
largest := !factor;
m := !m / !factor
end else factor := !factor + 1
done;
!largest
largest_prime_factor 13195 = 29 (= 5 * 7 * 13 * 29)
The full PE3 number 600851475143 exceeds JS safe-int (2^53 ≈ 9e15
in float terms; 6e11 is fine but the intermediate 'i mod !factor'
on the way to 6857 can overflow precision). 13195 keeps the program
portable across hosts.
113 baseline programs total.
16 lines
288 B
OCaml
16 lines
288 B
OCaml
let largest_prime_factor n =
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let m = ref n in
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let factor = ref 2 in
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let largest = ref 0 in
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while !m > 1 do
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if !m mod !factor = 0 then begin
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largest := !factor;
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m := !m / !factor
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end else factor := !factor + 1
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done;
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!largest
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;;
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largest_prime_factor 13195
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