Lecture 14

src/main/java/it/unimi/di/prog2/h14/IntGenerator.java

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+/*
+
+Copyright 2024 Massimo Santini
+
+This file is part of "Programmazione 2 @ UniMI" teaching material.
+
+This 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.
+
+This material 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 this file.  If not, see <https://www.gnu.org/licenses/>.
+
+*/
+
+package it.unimi.di.prog2.h14;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+/** Generator (in Liskov parlance) of the ints contained in a {@link List}. */
+public class IntGenerator implements Iterator<Integer> {
+
+  /** The list elements. */
+  private final List<Integer> els;
+
+  /** The position of the next element to return (if {@code idx < els.size()}. */
+  private int idx;
+
+  /**
+   * Builds an iterator (partial constructor, used just in {@link IntSet}).
+   *
+   * @param els the list of elements, must not be, or contain, {@code null}.
+   */
+  public IntGenerator(List<Integer> els) {
+    this.els = els;
+    this.idx = 0;
+  }
+
+  @Override
+  public boolean hasNext() {
+    return idx < els.size();
+  }
+
+  @Override
+  public Integer next() {
+    if (!hasNext()) throw new NoSuchElementException();
+    return els.get(idx++);
+  }
+}

src/main/java/it/unimi/di/prog2/h14/IntSet.java

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+/*
+
+Copyright 2024 Massimo Santini
+
+This file is part of "Programmazione 2 @ UniMI" teaching material.
+
+This 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.
+
+This material 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 this file.  If not, see <https://www.gnu.org/licenses/>.
+
+*/
+
+package it.unimi.di.prog2.h14;
+
+import it.unimi.di.prog2.h08.impl.EmptyException;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * {@code IntSet}s are mutable, unbounded sets of integers.
+ *
+ * <p>A typical IntSet is \( S = \{x_1, \ldots, x_n \} \).
+ */
+public class IntSet implements Iterable<Integer> {
+
+  /** The {@link List} containing this set elements. */
+  private final List<Integer> els;
+
+  /*
+   * AF: gli elementi dell'IntSet sono tutti e soli gli interi
+   *     contenuti nella lista; detto altrimenti,
+   *     S = { els.get(i) per 0 <= i < els.size() }
+   *
+   * RI: els != null
+   *     els non deve contenere null
+   *     els non deve contenere duplicati, detto altrimenti
+   *     se 0 <= i, j < els.size() e i != j allora els.get(i) != els.get(j)
+   *
+   */
+
+  private boolean repOk() {
+    for (int i = 0; i < els.size(); i++)
+      for (int j = 0; j < els.size(); j++)
+        if (i != j && els.get(i).equals(els.get(j))) return false;
+    return true;
+  }
+
+  /**
+   * Initializes this set to be empty.
+   *
+   * <p>Builds the set \( S = \varnothing \).
+   */
+  public IntSet() {
+    els = new ArrayList<>();
+    assert repOk();
+  }
+
+  /**
+   * A *copy constructor*.
+   *
+   * @param other the {@code IntSet} to copy from.
+   */
+  public IntSet(IntSet other) {
+    els = new ArrayList<Integer>(other.els);
+    assert repOk();
+  }
+
+  // Methods
+
+  /**
+   * Looks for a given element in this set.
+   *
+   * @param x the element to look for.
+   * @return the index where {@code x} appears in {@code els} if the element belongs to this set, or
+   *     -1
+   */
+  private int getIndex(int x) {
+    return els.indexOf(x);
+  }
+
+  /**
+   * Adds the given element to this set.
+   *
+   * <p>This method modifies the object, that is: \( S' = S \cup \{ x \} \).
+   *
+   * @param x the element to be added.
+   */
+  public void insert(int x) {
+    if (getIndex(x) < 0) els.add(x);
+    assert repOk();
+  }
+
+  /**
+   * Removes the given element from this set.
+   *
+   * <p>This method modifies the object, that is: \( S' = S \setminus \{ x \} \).
+   *
+   * @param x the element to be removed.
+   */
+  public void remove(int x) {
+    int i = getIndex(x);
+    if (i < 0) return;
+    int last = els.size() - 1;
+    els.set(i, els.get(last));
+    els.remove(last);
+    assert repOk();
+  }
+
+  /**
+   * Tells if the given element is in this set.
+   *
+   * <p>Answers the question \( x\in S \).
+   *
+   * @param x the element to look for.
+   * @return whether the given element belongs to this set, or not.
+   */
+  public boolean isIn(int x) {
+    return getIndex(x) != -1;
+  }
+
+  /**
+   * Returns the cardinality of this set.
+   *
+   * <p>Responds with \( |S| \).
+   *
+   * @return the size of this set.
+   */
+  public int size() {
+    return els.size();
+  }
+
+  /**
+   * Returns an element from this set.
+   *
+   * @return an arbitrary element from this set.
+   * @throws EmptyException if this set is empty.
+   */
+  public int choose() throws EmptyException {
+    if (els.isEmpty()) throw new EmptyException("Can't choose from an empty set");
+    return els.get(els.size() - 1);
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof IntSet)) return false;
+    IntSet other = (IntSet) obj;
+    if (els.size() != other.els.size()) return false;
+    for (int e : els) if (!other.isIn(e)) return false;
+    return true;
+  }
+
+  @Override
+  public int hashCode() {
+    els.sort(null); // benevolent side effect
+    return Objects.hash(els.size(), els);
+  }
+
+  @Override
+  public String toString() {
+    String lst = els.toString();
+    return "IntSet: {" + lst.substring(1, lst.length() - 1) + "}";
+  }
+
+  @Override
+  public Iterator<Integer> iterator() {
+    return new IntGenerator(els);
+  }
+}

src/main/java/it/unimi/di/prog2/h14/IntSetsClient.java

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+/*
+
+Copyright 2024 Massimo Santini
+
+This file is part of "Programmazione 2 @ UniMI" teaching material.
+
+This 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.
+
+This material 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 this file.  If not, see <https://www.gnu.org/licenses/>.
+
+*/
+
+package it.unimi.di.prog2.h14;
+
+import java.util.Scanner;
+
+/** Classe per il test di {@link IntSet} {@link IntGenerator}. */
+public class IntSetsClient {
+  private IntSetsClient() {}
+
+  /**
+   * Legge una sequenza di interi dal flusso di ingresso ed emette la loro somma nel flusso
+   * d'uscita.
+   *
+   * @param args non usato.
+   */
+  public static void main(String[] args) {
+    IntSet S = new IntSet();
+
+    try (Scanner s = new Scanner(System.in)) {
+      while (s.hasNextInt()) S.insert(s.nextInt());
+    }
+
+    int tot = 0;
+    for (int x : S) tot += x;
+    System.out.println(tot);
+  }
+}

src/main/java/it/unimi/di/prog2/h14/Primes.java

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+/*
+
+Copyright 2024 Massimo Santini
+
+This file is part of "Programmazione 2 @ UniMI" teaching material.
+
+This 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.
+
+This material 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 this file.  If not, see <https://www.gnu.org/licenses/>.
+
+*/
+
+package it.unimi.di.prog2.h14;
+
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+
+/** Iteratore che genera i numeri primi. */
+public class Primes implements Iterator<Integer> {
+
+  /*-
+   *  AF: il prossimo numero primo è il primo intero maggiore o uguale a
+   *      candidate che non sia divisibile per uno dei primi già restituiti da next,
+   *      contenuti in foundPrimes.
+   *
+   *  RI: - candidate è 2, oppure un numero dispari maggiore del più grande primo in
+   *        foundPrimes
+   *      - foundPrimes è vuoto, oppure contiene tutti i numeri primi miniori o uguali
+   *        a candidate che sono stati restituiti da next.
+   */
+
+  /** Il prossimo potenziale numero primo. */
+  private int candidate = 2;
+
+  /** L'elenco di primi restituiti da next. */
+  private final List<Integer> foundPrimes = new LinkedList<>();
+
+  @Override
+  public boolean hasNext() {
+    return true;
+  }
+
+  /**
+   * Verifica se {@code n} è divisibile per un dei primi in {@link #foundPrimes}.
+   *
+   * @param n il numero da verificare.
+   * @return {@code true} se {@code n} è divisibile per un dei primi già trovati.
+   */
+  private boolean isDivisibleByAFoundPrime(int n) {
+    for (int p : foundPrimes) {
+      if (n % p == 0) return true;
+      if (p * p > n) return false;
+    }
+    return false;
+  }
+
+  @Override
+  public Integer next() {
+    if (candidate == 2) {
+      foundPrimes.add(candidate);
+      candidate = 3;
+      return 2;
+    } else
+      for (int n = candidate; ; n += 2)
+        if (!isDivisibleByAFoundPrime(n)) {
+          foundPrimes.add(n);
+          candidate = n + 2;
+          return n;
+        }
+  }
+}

src/main/java/it/unimi/di/prog2/h14/package-info.java

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+/**
+ * Codice relativo alla lezione 14 per maggiori dettagli si veda il <a
+ * href="https://prog2.di.unimi.it/diario">diario del corso</a>.
+ */
+package it.unimi.di.prog2.h14;

tests/it/unimi/di/prog2/h14/IntSetsClient/expected-1.txt

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+10

tests/it/unimi/di/prog2/h14/IntSetsClient/expected-2.txt

@@ -0,0 +1 @@
+0

tests/it/unimi/di/prog2/h14/IntSetsClient/input-1.txt

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+1
+2
+3
+4