Added solutions and fixed the clients

src/main/java/it/unimi/di/prog2/e09/PolyClient.java

@@ -30,27 +30,26 @@ private PolyClient() {}
   /**
    * Tests some methods of {@link Poly}.
    *
-   * <p>Starting from term \( t_0 = x + 1 \) reads a list of \( t_i \) of terms from the standard
-   * input, given as a (coefficient, degree) pairs, and computes the polynomial \( t_0 \cdot t_1
-   * \cdot t_2 \cdots \), emitting in the standard output the pairs "coefficient degree" for every
-   * term in the result (in increasing order of degree).
+   * <p>Starting from term \( t_0 = 0 \) reads a list of \( t_i \) of terms from the standard input,
+   * given as a (coefficient, degree) pairs, and computes the polynomial \( t_0 + t_1 + t_2 \cdots
+   * \), emitting in the standard output the pairs "coefficient degree" for every term in the result
+   * (in increasing order of degree).
    *
    * @param args not used.
    */
 
   /*- Uncomment the main method once you have implemented the add method in Poly class
 
   public static void main(String[] args) {
-    Poly result = null;
-    Poly xp1 = new Poly(1, 1).add(new Poly(-1, 0));
+    Poly result = new Poly();
     try (Scanner s = new Scanner(System.in)) {
       while (s.hasNextInt()) {
         Poly term = new Poly(s.nextInt(), s.nextInt());
-        if (result == null) result = term;
-        else result = result.mul(xp1).add(term);
+        result = result.add(term);
       }
       for (int d = 0; d <= result.degree(); d++) System.out.println(result.coeff(d) + " " + d);
     }
   }
+
   */
 }

src/main/java/it/unimi/di/prog2/e09/SparsePolyClient.java

@@ -31,26 +31,25 @@ private SparsePolyClient() {}
    * Tests some methods of {@link SparsePoly}.
    *
    * <p>Starting from term \( t_0 = x + 1 \) reads a list of \( t_i \) of terms from the standard
-   * input, given as a (coefficient, degree) pairs, and computes the polynomial \( t_0 \cdot t_1
-   * \cdot t_2 \cdots \), emitting in the standard output the pairs "coefficient degree" for every
-   * term in the result (in increasing order of degree).
+   * input, given as a (coefficient, degree) pairs, and computes the polynomials \( p_{i+1} = p_i
+   * \codt t_i + t_i \) emitting in the standard output the pairs "coefficient degree" for every
+   * term (in increasing order of degree) of the last computed polynomial.
    *
    * @param args not used.
    */
 
   /*- Uncomment the main method once you have implemented the SparsePoly class
 
   public static void main(String[] args) {
-    SparsePoly result = null;
-    SparsePoly xp1 = new SparsePoly(1, 1).add(new SparsePoly(-1, 0));
+    SparsePoly result = new SparsePoly(1, 1).add(new SparsePoly(-1, 0));
     try (Scanner s = new Scanner(System.in)) {
       while (s.hasNextInt()) {
         SparsePoly term = new SparsePoly(s.nextInt(), s.nextInt());
-        if (result == null) result = term;
-        else result = result.mul(xp1).add(term);
+        result = result.mul(term).add(term);
       }
       for (int d = 0; d <= result.degree(); d++) System.out.println(result.coeff(d) + " " + d);
     }
   }
+
   */
 }

src/main/java/it/unimi/di/prog2/h09/Poly.java

@@ -130,7 +130,7 @@ public Poly add(Poly q) throws NullPointerException {
    * @throws NullPointerException if {@code q} is {@code null}.
    */
   public Poly mul(Poly q) throws NullPointerException {
-    if (q == null) throw new NullPointerException();
+    if (q == null) throw new NullPointerException("The polynomial must not be null.");
     if ((q.degree == 0 && q.coefficient[0] == 0) || (degree == 0 && coefficient[0] == 0))
       return new Poly();
     Poly result = new Poly(degree + q.degree);
@@ -150,7 +150,7 @@ public Poly mul(Poly q) throws NullPointerException {
    * @throws NullPointerException if {@code q} is {@code null}.
    */
   public Poly sub(Poly q) throws NullPointerException {
-    if (q == null) throw new NullPointerException();
+    if (q == null) throw new NullPointerException("The polynomial must not be null.");
     return add(q.minus());
   }
 

src/main/java/it/unimi/di/prog2/s09/Poly.java

@@ -0,0 +1,165 @@
+/*
+
+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.s09;
+
+import it.unimi.di.prog2.h08.impl.NegativeExponentException;
+import java.util.Objects;
+
+/**
+ * {@code Poly}s are immutable polynomials with integer coefficients.
+ *
+ * <p>A typical {@code Poly} is \( p = c_0 + c_1 x + c_2 x^2 + \cdots + c_n x^n \).
+ */
+public class Poly { // we don't extend Cloneable, see EJ 3.13
+
+  /** The array of coefficients, the {@code coeff[i]} is the coefficient of \( x^i \). */
+  private final int[] coefficient;
+
+  /** Initializes this to be the zero polynomial, that is \( p = 0 \). */
+  public Poly() {
+    coefficient = new int[1];
+  }
+
+  /**
+   * Initializes this to be the polynomial \(p = cx^n\).
+   *
+   * @param c the coefficient.
+   * @param n the degree.
+   * @throws NegativeExponentException if {@code n} &lt; 0.
+   */
+  public Poly(int c, int n) throws NegativeExponentException {
+    if (n < 0)
+      throw new NegativeExponentException("Can't create a monomial with negative exponent");
+    coefficient = new int[n + 1];
+    coefficient[n] = c;
+  }
+
+  /**
+   * Initializes a polynomial of given degree (with all coefficients equal to 0).
+   *
+   * @param n the degree, must be non-negative.
+   */
+  private Poly(int n) {
+    coefficient = new int[n + 1];
+  }
+
+  /**
+   * Returns the degree of this polynomial.
+   *
+   * @return the largest exponent with a non-zero coefficient; returns 0 if this is the zero {@code
+   *     Poly}.
+   */
+  public int degree() {
+    return coefficient.length - 1;
+  }
+
+  /**
+   * Returns the coefficient of the term of given exponent.
+   *
+   * @param d the exponent of the term to consider.
+   * @return the coefficient of the considered term.
+   */
+  public int coeff(int d) {
+    if (d < 0 || d >= coefficient.length) return 0;
+    else return coefficient[d];
+  }
+
+  /**
+   * Performs polynomial addition.
+   *
+   * <p>If \( p \) is this polynomial, returns \( p + q \).
+   *
+   * @param q the polynomial to add to this one.
+   * @return the sum among this and the given polynomial.
+   * @throws NullPointerException if {@code q} is {@code null}.
+   */
+  public Poly add(Poly q) throws NullPointerException {
+    Objects.requireNonNull(q, "The polynomial must not be null.");
+    final Poly larger, smaller;
+    if (degree() > q.degree()) {
+      larger = this;
+      smaller = q;
+    } else {
+      larger = q;
+      smaller = this;
+    }
+    int resultDegree = larger.degree();
+    if (degree() == q.degree()) {
+      for (int k = degree(); k > 0; k--)
+        if (coefficient[k] + q.coefficient[k] != 0) break;
+        else resultDegree--;
+    }
+    Poly result = new Poly(resultDegree); // get a new Poly
+    int i;
+    for (i = 0; i <= smaller.degree() && i <= resultDegree; i++)
+      result.coefficient[i] = smaller.coefficient[i] + larger.coefficient[i];
+    for (int j = i; j <= resultDegree; j++) result.coefficient[j] = larger.coefficient[j];
+    return result;
+  }
+
+  /**
+   * Performs polynomial multiplication.
+   *
+   * <p>If \( p \) is this polynomial, returns \( p q \).
+   *
+   * @param q the polynomial to multiply by this one.
+   * @return the product among this and the given polynomial.
+   * @throws NullPointerException if {@code q} is {@code null}.
+   */
+  public Poly mul(Poly q) throws NullPointerException {
+    Objects.requireNonNull(q, "The polynomial must not be null.");
+    if ((q.degree() == 0 && q.coefficient[0] == 0) || (degree() == 0 && coefficient[0] == 0))
+      return new Poly();
+    Poly r = new Poly(degree() + q.degree());
+    for (int i = 0; i <= degree(); i++)
+      for (int j = 0; j <= q.degree(); j++)
+        r.coefficient[i + j] = r.coefficient[i + j] + coefficient[i] * q.coefficient[j];
+    return r;
+  }
+
+  /**
+   * Performs polynomial subtraction.
+   *
+   * <p>If \( p \) is this polynomial, returns \( p - q \).
+   *
+   * @param q the polynomial to subtract from this one.
+   * @return the subtraction among this and the given polynomial.
+   * @throws NullPointerException if {@code q} is {@code null}.
+   */
+  public Poly sub(Poly q) throws NullPointerException {
+    Objects.requireNonNull(q, "The polynomial must not be null.");
+    return add(q.minus());
+  }
+
+  /**
+   * Returns the negate polynomial.
+   *
+   * <p>If \( p \) is this polynomial, returns \( -p \).
+   *
+   * @return this polynomial multiplied by \( -1 \).
+   */
+  public Poly minus() {
+    Poly r = new Poly(degree());
+    for (int i = 0; i <= degree(); i++) r.coefficient[i] = -coefficient[i];
+    return r;
+  }
+}

src/main/java/it/unimi/di/prog2/s09/PolyClient.java

@@ -0,0 +1,52 @@
+/*
+
+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.s09;
+
+import java.util.Scanner;
+
+/** A class to test some methods of {@link Poly}. */
+public class PolyClient {
+
+  /** . */
+  private PolyClient() {}
+
+  /**
+   * Tests some methods of {@link Poly}.
+   *
+   * <p>Starting from term \( t_0 = 0 \) reads a list of \( t_i \) of terms from the standard input,
+   * given as a (coefficient, degree) pairs, and computes the polynomial \( t_0 + t_1 + t_2 \cdots
+   * \), emitting in the standard output the pairs "coefficient degree" for every term in the result
+   * (in increasing order of degree).
+   *
+   * @param args not used.
+   */
+  public static void main(String[] args) {
+    Poly result = new Poly();
+    try (Scanner s = new Scanner(System.in)) {
+      while (s.hasNextInt()) {
+        Poly term = new Poly(s.nextInt(), s.nextInt());
+        result = result.add(term);
+      }
+      for (int d = 0; d <= result.degree(); d++) System.out.println(result.coeff(d) + " " + d);
+    }
+  }
+}