Skip to content

Fix nthPermutation lexicographic order #10922

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
AaritPanda-git wants to merge 1 commit into
base: master
Choose a base branch
from
+50 −4
Open

Fix nthPermutation lexicographic order #10922

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
54 changes: 50 additions & 4 deletions std/algorithm/sorting.d
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -77,7 +77,7 @@ T2=$(TR $(TDNW $(LREF $1)) $(TD $+))
*/
module std.algorithm.sorting;

import std.algorithm.mutation : SwapStrategy;
import std.algorithm.mutation : SwapStrategy, reverse;
import std.functional : unaryFun, binaryFun;
import std.range.primitives;
import std.typecons : Flag, No, Yes;
Expand Down Expand Up @@ -5025,6 +5025,7 @@ bool nthPermutationImpl(Range)
(auto ref Range range, ulong perm)
if (isRandomAccessRange!Range && hasLength!Range)
{

import std.range.primitives : ElementType;
import std.numeric : decimalToFactorial;

Expand All @@ -5037,10 +5038,20 @@ if (isRandomAccessRange!Range && hasLength!Range)
return false;
}

if (idx < range.length)
{
reverse(fac[0 .. idx]);
// Preserve leading zero digits in the Lehmer code to ensure lexicographic order

reverse(fac[0 .. range.length]);
}

size_t len = range.length;

ElementType!Range tmp;
size_t i = 0;

for (; i < idx; ++i)
for (; i < len; ++i)
{
size_t re = fac[i];
tmp = range[re + i];
Expand All @@ -5055,6 +5066,41 @@ if (isRandomAccessRange!Range && hasLength!Range)
}

///
pure @safe unittest
{
auto src = [0, 1, 2];
auto rslt = [0, 2, 1];

src = nthPermutation(src, 1);
assert(src == rslt);
}
pure @safe unittest
{
auto src = [0, 1, 2, 3];
auto rslt = [0, 3, 1, 2];

src = nthPermutation(src, 4);
assert(src == rslt);
}
pure @safe unittest
{
auto src = [0, 1, 2];
auto rslt = [0, 2, 1];

bool worked = nthPermutationImpl(src, 1);
assert(worked);
assert(src == rslt);
}
pure @safe unittest
{
auto src = [0, 1, 2, 3];
auto rslt = [0, 3, 1, 2];

bool worked = nthPermutationImpl(src, 4);
assert(worked);
assert(src == rslt);
}

pure @safe unittest
{
auto src = [0, 1, 2, 3, 4, 5, 6];
Expand All @@ -5076,7 +5122,7 @@ pure @safe unittest
pure @safe unittest
{
auto src = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
auto rslt = [4, 0, 6, 2, 1, 3, 5, 7, 8, 9, 10];
auto rslt = [0, 1, 2, 3, 8, 4, 10, 6, 5, 7, 9];

src = nthPermutation(src, 2982);
assert(src == rslt);
Expand All @@ -5097,7 +5143,7 @@ pure @safe unittest
import std.meta : AliasSeq;

auto src = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
auto rsl = [4, 0, 6, 2, 1, 3, 5, 7, 8, 9, 10];
auto rsl = [0, 1, 2, 3, 8, 4, 10, 6, 5, 7, 9];

foreach (T; AliasSeq!(
DummyRange!(ReturnBy.Reference, Length.Yes, RangeType.Random, int[]),
Expand Down