giles
edbb03e205
Some checks failed
Test, Build, and Deploy / test-build-deploy (push) Failing after 21s
Hoare quickselect with Lomuto partition: recursively narrows the
range to whichever side contains the kth index. Mutates the array
in place via .(i)<-v. The median (k=4) of [7;2;9;1;5;6;3;8;4] is 5.
let rec quickselect arr lo hi k =
if lo = hi then arr.(lo)
else begin
let pivot = arr.(hi) in
let i = ref lo in
for j = lo to hi - 1 do
if arr.(j) < pivot then begin
let t = arr.(!i) in
arr.(!i) <- arr.(j); arr.(j) <- t;
i := !i + 1
end
done;
...
end
Exercises array literal syntax + in-place mutation in the same
program, ensuring [|...|] yields a mutable backing.
138 baseline programs total.
26 lines
569 B
OCaml
26 lines
569 B
OCaml
let rec quickselect arr lo hi k =
|
|
if lo = hi then arr.(lo)
|
|
else begin
|
|
let pivot = arr.(hi) in
|
|
let i = ref lo in
|
|
for j = lo to hi - 1 do
|
|
if arr.(j) < pivot then begin
|
|
let t = arr.(!i) in
|
|
arr.(!i) <- arr.(j);
|
|
arr.(j) <- t;
|
|
i := !i + 1
|
|
end
|
|
done;
|
|
let t = arr.(!i) in
|
|
arr.(!i) <- arr.(hi);
|
|
arr.(hi) <- t;
|
|
if !i = k then arr.(!i)
|
|
else if !i < k then quickselect arr (!i + 1) hi k
|
|
else quickselect arr lo (!i - 1) k
|
|
end
|
|
|
|
;;
|
|
|
|
let a = [|7; 2; 9; 1; 5; 6; 3; 8; 4|] in
|
|
quickselect a 0 8 4
|