/*
* Redberry: symbolic tensor computations.
*
* Copyright (c) 2010-2013:
* Stanislav Poslavsky <stvlpos@mail.ru>
* Bolotin Dmitriy <bolotin.dmitriy@gmail.com>
*
* This file is part of Redberry.
*
* Redberry is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Redberry is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Redberry. If not, see <http://www.gnu.org/licenses/>.
*/
package cc.redberry.core.groups.permutations;
import cc.redberry.core.utils.BitArray;
/**
* @author Dmitry Bolotin
* @author Stanislav Poslavsky
*/
public class Combinatorics {
/**
* Tests whether the specified array satisfies the one-line notation for permutations
*
* @param permutation array to be tested
* @return {@code true} if specified array satisfies the one-line notation for permutations and {@code false} if
* not
*/
public static boolean testPermutationCorrectness(int[] permutation) {
int length = permutation.length;
BitArray checked = new BitArray(length);
for (int i = 0; i < length; ++i) {
if (permutation[i] >= length || permutation[i] < 0)
return false;
if (checked.get(permutation[i]))
return false;
checked.set(permutation[i]);
}
return checked.isFull();
}
private static final Permutation[] cachedIdentities = new Permutation[64];
private static Permutation createIdentity(int length) {
int[] array = new int[length];
for (int i = 0; i < length; ++i)
array[i] = i;
return new Permutation(true, false, array);
}
public static Permutation getIdentity(int length) {
if (cachedIdentities.length >= length)
return createIdentity(length);
if (cachedIdentities[length] == null)
synchronized (cachedIdentities) {
if (cachedIdentities[length] == null)
cachedIdentities[length] = createIdentity(length);
}
return cachedIdentities[length];
}
}