code: ///////////////////////////////////////////////////////////////////////////
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  //                  / /   ____  ____ _(_)____/ | / / ____/               //
  //                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
  //                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
  //               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
  //                           /____/                                      //
  //                                                                       //
  //               The Next Generation Logic Library                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  //                                                                       //
  //  Copyright 2015-20xx Christoph Zengler                                //
  //                                                                       //
  //  Licensed under the Apache License, Version 2.0 (the "License");      //
  //  you may not use this file except in compliance with the License.     //
  //  You may obtain a copy of the License at                              //
  //                                                                       //
  //  http://www.apache.org/licenses/LICENSE-2.0                           //
  //                                                                       //
  //  Unless required by applicable law or agreed to in writing, software  //
  //  distributed under the License is distributed on an "AS IS" BASIS,    //
  //  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
  //  implied.  See the License for the specific language governing        //
  //  permissions and limitations under the License.                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  
  package org.logicng.collections;
  
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Comparator;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  /**
   * A simple vector implementation (inspired by MiniSat, CleaneLing, Sat4J).
   * @param <T> the type of the elements
   * @version 1.0
   * @since 1.0
   */
  public final class LNGVector<T> implements Iterable<T> {
  
      private T[] elements;
      private int size;
  
      /**
       * Creates a vector with an initial capacity of 5 elements.
       */
      public LNGVector() {
          this(5);
      }
  
      /**
       * Creates a vector with a given capacity.
       * @param size the capacity of the vector.
       */
      @SuppressWarnings("unchecked")
      public LNGVector(final int size) {
          this.elements = (T[]) new Object[size];
      }
  
      /**
       * Creates a vector with a given capacity and a given initial element.
       * @param size the capacity of the vector
       * @param pad  the initial element
       */
      @SuppressWarnings("unchecked")
      public LNGVector(final int size, final T pad) {
          this.elements = (T[]) new Object[size];
          Arrays.fill(this.elements, pad);
          this.size = size;
      }
  
      /**
       * Creates a vector with the given elements.
       * @param elems the elements
       */
      @SafeVarargs
      public LNGVector(final T... elems) {
          this.elements = Arrays.copyOf(elems, elems.length);
          this.size = elems.length;
      }
  
      /**
       * Creates a vector with the given elements
       * @param elems the elements
       */
      @SuppressWarnings("unchecked")
      public LNGVector(final Collection<T> elems) {
          this.elements = (T[]) new Object[elems.size()];
          int count = 0;
          for (final T e : elems) {
              this.elements[count++] = e;
          }
          this.size = elems.size();
      }
  
      /**
       * Returns whether the vector is empty or not.
       * @return {@code true} if the vector is empty, {@code false} otherwise
       */
      public boolean empty() {
          return this.size == 0;
      }
  
      /**
       * Returns the size of the vector.
       * @return the size of the vector
       */
      public int size() {
          return this.size;
      }
  
      /**
       * Returns the last element of the vector and leaves it on the vector.
       * @return the last element of the vector
       */
      public T back() {
          return this.elements[this.size - 1];
      }
  
      /**
       * Pushes an element at the end of the vector.
       * @param element the element
       */
      public void push(final T element) {
          final int newSize = this.size + 1;
          this.ensure(newSize);
          this.elements[this.size++] = element;
      }
  
      /**
       * Pushes an element and assumes that there is enough space on the vector.
       * @param element the element to push
       * @throws ArrayIndexOutOfBoundsException if there was not enough space on the vector
       */
      public void unsafePush(final T element) {
          this.elements[this.size++] = element;
      }
  
      /**
       * Returns the element at a given position in the vector.
       * @param position the position
       * @return the element at the position
       * @throws ArrayIndexOutOfBoundsException if the position is not found in the vector
       */
      public T get(final int position) {
          return this.elements[position];
      }
  
      /**
       * Sets an element at a given position in the vector.
       * @param position the position
       * @param element  the element
       * @throws ArrayIndexOutOfBoundsException if the position is not found in the vector
       */
      public void set(final int position, final T element) {
          this.elements[position] = element;
      }
  
      /**
       * Removes the last element of the vector.
       */
      public void pop() {
          this.elements[--this.size] = null;
      }
  
      /**
       * Shrinks the vector to a given size if the new size is less than the current size.  Otherwise, the size remains
       * the same.
       * @param newSize the new size
       */
      public void shrinkTo(final int newSize) {
          if (newSize < this.size) {
              for (int i = this.size; i > newSize; i--) {
                  this.elements[i - 1] = null;
              }
              this.size = newSize;
          }
      }
  
      /**
       * Grows the vector to a new size and initializes the new elements with a given value.
       * @param size the new size
       * @param pad  the value for new elements
       */
      public void growTo(final int size, final T pad) {
          if (this.size >= size) {
              return;
          }
          this.ensure(size);
          for (int i = this.size; i < size; i++) {
              this.elements[i] = pad;
          }
          this.size = size;
      }
  
      /**
       * Grows the vector to a new size and initializes the new elements with {@code null}.
       * @param size the new size
       */
      public void growTo(final int size) {
          if (this.size >= size) {
              return;
          }
          this.ensure(size);
          this.size = size;
      }
  
      /**
       * Removes a given number of elements from the vector.
       * @param num the number of elements to remove.
       * @throws ArrayIndexOutOfBoundsException if the number of elements to remove is larger than the size of the vector
       */
      public void removeElements(final int num) {
          int n = num;
          while (n-- > 0) {
              this.elements[--this.size] = null;
          }
      }
  
      /**
       * Removes the first occurrence of a given element from the vector (the element is compared by {@code equals}).
       * @param element the element to remove
       * @return {@code true} if the element was removed, {@code false} if the element was not in the vector
       */
      public boolean remove(final T element) {
          for (int i = 0; i < this.size; i++) {
              if (this.elements[i].equals(element)) {
                  System.arraycopy(this.elements, i + 1, this.elements, i, this.size - (i + 1));
                  this.size--;
                  return true;
              }
          }
          return false;
      }
  
      /**
       * Replaces the contents of this vector with the contents of another vector in-place.
       * @param other the other vector
       * @throws IllegalArgumentException if you try to replace a vector with itself
       */
      @SuppressWarnings("unchecked")
      public void replaceInplace(final LNGVector<? extends T> other) {
          if (this == other) {
              throw new IllegalArgumentException("cannot replace a vector in-place with itself");
          }
          this.elements = (T[]) new Object[other.size()];
          for (int i = 0; i < other.size(); i++) {
              this.elements[i] = other.get(i);
          }
          this.size = other.size;
      }
  
      /**
       * Clears the vector.  This method only sets the size to 0.  The elements are not nulled out.
       * Use {@link #release()} for this purpose.
       */
      public void clear() {
          this.size = 0;
      }
  
      /**
       * Clears the vector and sets all elements to {@code null}.
       */
      public void release() {
          Arrays.fill(this.elements, null);
          this.size = 0;
      }
  
      /**
       * Sorts this vector with a given comparator (with JDK sorting).
       * @param comparator the comparator
       */
      public void sort(final Comparator<T> comparator) {
          Arrays.sort(this.elements, 0, this.size, comparator);
      }
  
      /**
       * Sorts this vector with a given comparator (with manual implemented merge sort).  This method is required for
       * sorting clauses based on activity, since not all requirements of the JDK sorting are met.
       * @param comparator the comparator
       */
      public void manualSort(final Comparator<T> comparator) {
          this.sort(this.elements, 0, this.size, comparator);
      }
  
      /**
       * Selection sort implementation for a given array.
       * @param array the array
       * @param start the start index for sorting
       * @param end   the end index for sorting
       * @param lt    the comparator for elements of the array
       */
      private void selectionSort(final T[] array, final int start, final int end, final Comparator<T> lt) {
          int i;
          int j;
          int bestI;
          T tmp;
          for (i = start; i < end; i++) {
              bestI = i;
              for (j = i + 1; j < end; j++) {
                  if (lt.compare(array[j], array[bestI]) < 0) {
                      bestI = j;
                  }
              }
              tmp = array[i];
              array[i] = array[bestI];
              array[bestI] = tmp;
          }
      }
  
      /**
       * Merge sort implementation for a given array.
       * @param array the array
       * @param start the start index for sorting
       * @param end   the end index for sorting
       * @param lt    the comparator for elements of the array
       */
      private void sort(final T[] array, final int start, final int end, final Comparator<T> lt) {
          if (start == end) {
              return;
          }
          if ((end - start) <= 15) {
              this.selectionSort(array, start, end, lt);
          } else {
              final T pivot = array[start + ((end - start) / 2)];
              T tmp;
              int i = start - 1;
              int j = end;
              while (true) {
                  do {
                      i++;
                  }
                  while (lt.compare(array[i], pivot) < 0);
                  do {
                      j--;
                  }
                  while (lt.compare(pivot, array[j]) < 0);
                  if (i >= j) {
                      break;
                  }
                  tmp = array[i];
                  array[i] = array[j];
                  array[j] = tmp;
              }
              this.sort(array, start, i, lt);
              this.sort(array, i, end, lt);
          }
      }
  
      /**
       * Sorts this vector in reverse order.
       * @param comparator the comparator
       */
      public void sortReverse(final Comparator<T> comparator) {
          this.sort(comparator);
          for (int i = 0; i < this.size / 2; i++) {
              final T temp = this.elements[i];
              this.elements[i] = this.elements[this.size - i - 1];
              this.elements[this.size - i - 1] = temp;
          }
      }
  
      /**
       * Ensures that this vector has the given size.  If not - the size is doubled and the old elements are copied.
       * @param newSize the size to ensure
       */
      @SuppressWarnings("unchecked")
      private void ensure(final int newSize) {
          if (newSize >= this.elements.length) {
              final T[] newArray = (T[]) new Object[Math.max(newSize, this.size * 2)];
              System.arraycopy(this.elements, 0, newArray, 0, this.size);
              this.elements = newArray;
          }
      }
  
      @Override
      public Iterator<T> iterator() {
          return new Iterator<T>() {
              private int i;
  
              @Override
              public boolean hasNext() {
                  return i < size;
              }
  
              @Override
              public T next() {
                  if (i == size) {
                      throw new NoSuchElementException();
                  }
                  return elements[i++];
              }
  
              @Override
              public void remove() {
                  throw new UnsupportedOperationException();
              }
          };
      }
  
      @Override
      public String toString() {
          final StringBuilder sb = new StringBuilder("[");
          for (int i = 0; i < this.size; i++) {
              sb.append(this.elements[i]);
              if (i != this.size - 1) {
                  sb.append(", ");
              }
          }
          sb.append("]");
          return sb.toString();
      }
  }
  