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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2008 The Closure Compiler Authors.
 *
 * 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 com.google.javascript.jscomp.graph;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Set;

/**
 * Union-Find is a classical algorithm used to find connected components in graph theory.
 *
 * Each equivalence class has a representative element that is chosen arbitrarily and is used to
 * determine if two elements are members of the same class.
 *
 * See algorithmist for more detail.
 *
 * @param  element type
 */
@GwtCompatible
public interface UnionFind {

  /**
   * Adds the given element to a new set if it is not already in a set.
   *
   * @throws UnsupportedOperationException if the add operation is not
   *     supported by this union-find.
   */
  public void add(E e);

  /**
   * Unions the equivalence classes of {@code a} and {@code b} and returns the representative of the
   * resulting equivalence class. The elements will be added if they are not already present.
   *
   * @throws UnsupportedOperationException if the add operation is not supported by this union-find.
   */
  @CanIgnoreReturnValue
  public E union(E a, E b);

  /** Returns the representative of the equivalence class of {@code e}. */
  public E find(E e);

  /**
   * Returns true if {@code a} and {@code b} belong to the same equivalence
   * class.
   *
   * @throws IllegalArgumentException if any argument is not an element of this
   *     structure.
   */
  public boolean areEquivalent(E a, E b);

  /** Returns an unmodifiable set of all elements added to the UnionFind. */
  public Set elements();

  /**
   * Returns an immutable collection containing all equivalence classes. The returned collection
   * represents a snapshot of the current state and will not reflect changes made to the data
   * structure.
   */
  public ImmutableList> allEquivalenceClasses();

  /**
   * Returns the elements in the same equivalence class as {@code value}.
   *
   * @return an unmodifiable view. As equivalence classes are merged, this set
   *     will reflect those changes.
   * @throws IllegalArgumentException if a requested element does not belong
   *     to the structure.
   */
  public Set findAll(final E value);

}