package algs34; import java.util.*; import stdlib.*; /* * Complete the methods o
ID: 3919613 • Letter: P
Question
package algs34;
import java.util.*;
import stdlib.*;
/*
* Complete the methods of MyFB so that it works.
* Each method must work in the worst case time given below (assuming uniform hashing and ignoring string lengths):
*
* addPerson must take constant time
*
* addFriendship must take constant time
*
* queryFriendship must take constant time
*
* removeFriendship should take constant time
*
* lookupFriends should take time proportional to the number of
* friends that the named person has (or less)
*
* Your solution should use a single field of type
*
* HashMap<Person,HashSet<Person>>
*
* You will need to add hashCode and equals methods to the Person class.
* To increase the avalance effect, consider a hash function that utilizes
* primes, for example:
*
* public int hashCode() {
* int result = 17;
* result = 37*result + var1;
* result = 37*result + var2;
* result = 37*result + var3;
* return result;
* }
*
* Don't change the first line of any method given below.
* The names and types of the methods should not change.
* I will run you MyFB class using my own main method.
*
* You can add more classes too. Just put them all in this file, inside MyFB.
* Any classes you add should be "static" and not "public".
* You can import/use any file in the java APIs.
* You can import/use any file in the algs packages.
*
* You do not need to implement a hash table for this assignment.
* You can use java.util.HashMap, java.util.HashSet, or the implementations in algs34.
*
* You do not need to implement an iterable object.
* You can use algs13.Queue.
* Also note that all of the Map implementations we have looked at create an iterable
* object via the keys() method.
*
*
* Here is an example session:
*
* INPUT OUTPUT
*
* p john 8
* p mike 7
* p sara 9
* p jane 5
* f mike 7 jane 5
* f mike 7 sara 9
* f jane 5 john 8
* l jane 5 mike 7 john 8
* l john 8 jane 5
* u mike 7 jane 5
* l jane 5 john 8
* q mike 7 sara 9 yes
* q sara 9 mike 7 yes
* q sara 9 mike 23 no
* q sara 9 sara 9 no
*
* Note that friendship is symmetric and irreflexive.
* So if a/b are friends, then so are b/a.
* And no one is their own friend.
*
* Put the following in a file "input.txt" to run this test:
p john 8
p mike 7
p sara 9
p jane 5
f mike 7 jane 5
f mike 7 sara 9
f jane 5 john 8
l jane 5
l john 8
u mike 7 jane 5
l jane 5
q mike 7 sara 9
q sara 9 mike 7
q sara 9 mike 23
q sara 9 sara 9
*/
public class MyFB {
public static boolean DEBUG = true;
public static Person makePerson (In in) {
try {
String name = in.readString ();
int age = in.readInt ();
return makePerson (name, age);
} catch (java.util.InputMismatchException e) {
StdOut.println ("Input format error");
return null;
}
}
public static Person makePerson (String name, int age) {
return new Person (name, age);
}
static class Person {
String name;
int age;
public Person (String name, int age) {
this.name = name;
this.age = age;
}
public String toString () {
return name + " " + age;
}
@Override
public boolean equals (Object obj) {
// TODO
return true;
}
@Override
public int hashCode () {
// TODO
return 1293879128;
}
}
HashMap<Person,HashSet<Person>> map = new HashMap<>();
// a person "exists" after they are added using addPerson
// addPerson does nothing if p already exists
public void addPerson (Person p) {
// TODO
if (DEBUG) { StdOut.format ("P %s: %s ", p, map); }
}
// addFriendship does nothing if p1 and p2 are already friends or if one does not exist
public void addFriendship (Person p1, Person p2) {
// TODO
if (DEBUG) { StdOut.format ("F %s %s: %s ", p1, p2, map); }
}
// removeFriendship does nothing if p1 and p2 are not friends or if one does not exist
public void removeFriendship (Person p1, Person p2) {
// TODO
if (DEBUG) { StdOut.format ("U %s %s: %s ", p1, p2, map); }
}
// queryFriendship returns false if p1 and p2 are not friends or if one does not exist
public boolean queryFriendship (Person p1, Person p2) {
if (DEBUG) { StdOut.format ("Q %s %s: ", p1, p2); }
// TODO
return false;
}
// lookupFriends returns null or empty iterable if p does not exists
public Iterable<Person> lookupFriends (Person p) {
if (DEBUG) { StdOut.format ("L %s:", p); }
// TODO
return null;
}
public static void hashTest () {
Trace.showBuiltInObjects (true);
//Trace.run ();
Person x = makePerson ("bob", 27);
Person y = makePerson ("bob", 27);
Boolean eq = x.equals(y);
Boolean hash = x.hashCode() == y.hashCode();
StdOut.println(x.toString() + " ("+x.hashCode()+") == " + y.toString() + " ("+y.hashCode()+")");
StdOut.println( " Equal Test: " + (eq ? "equal" : "not equal") );
StdOut.println( " Hash Test: " + (hash ? "equal" : "not equal") );
x = makePerson ("mike", 27);
y = makePerson ("john", 29);
eq = x.equals(y);
hash = x.hashCode() == y.hashCode();
StdOut.println(x.toString() + " ("+x.hashCode()+") == " + y.toString() + " ("+y.hashCode()+")");
StdOut.println( " Equal Test: " + (eq ? "equal" : "not equal") );
StdOut.println( " Hash Test: " + (hash ? "equal" : "not equal") );
}
public static void main (String[] args) {
Trace.showBuiltInObjects (true);
//Trace.run ();
hashTest();
/*
* The first line below causes "in" to read from the console. You can
* change this to read from a file, by using something like the line
* below, where "input.txt" is a file you create in your eclipse
* workspace. The file should be in the same folder that contains "src"
* "bin" and "lib":
*/
//In[] inputFiles = new In[] { new In () }; // from console
In[] inputFiles = new In[] { new In ("input.txt") }; // from file
//In[] inputFiles = new In[] { new In ("input.txt"), new In () }; // from file, then console
MyFB fb = new MyFB ();
StdOut.println (" ");
StdOut.println ("Enter one of the following:");
StdOut.println (" P name age -- add person");
StdOut.println (" F name1 age1 name2 age2 -- add friendship");
StdOut.println (" U name1 age1 name2 age2 -- remove friendship");
StdOut.println (" Q name1 age1 name2 age2 -- query friendship");
StdOut.println (" L name age -- lookup friends");
StdOut.println (" R -- restart");
StdOut.println (" X -- exit ");
for (In in : inputFiles) {
while (in.hasNextLine ()) {
String action;
try {
action = in.readString ();
} catch (NoSuchElementException e) { continue; }
//StdOut.println (action); // while debugging, print debugging info here! You can print maps, sets, lists.
switch (action) {
case "P":
case "p": {
Person p = makePerson (in);
fb.addPerson (p);
break;
}
case "F":
case "f": {
Person p1 = makePerson (in);
Person p2 = makePerson (in);
fb.addFriendship (p1, p2);
break;
}
case "U":
case "u": {
Person p1 = makePerson (in);
Person p2 = makePerson (in);
fb.removeFriendship (p1, p2);
//Trace.draw ();
break;
}
case "Q":
case "q": {
Person p1 = makePerson (in);
Person p2 = makePerson (in);
boolean result = fb.queryFriendship (p1, p2);
StdOut.println (result ? "Yes" : "No");
break;
}
case "L":
case "l": {
Person p = makePerson (in);
Iterable<Person> result = fb.lookupFriends (p);
if (result != null) {
for (Person friend : result) {
StdOut.print (friend);
StdOut.print (" ");
}
}
StdOut.println ();
break;
}
case "R":
case "r":
fb = new MyFB ();
break;
case "X":
case "x":
System.exit (0);
}
}
}
}
}
Explanation / Answer
package algs34;
import java.util.*;
import stdlib.*;
public class MyFB {
public static boolean DEBUG = true;
public static Person makePerson (In in) {
try {
String name = in.readString ();
int age = in.readInt ();
return makePerson (name, age);
} catch (java.util.InputMismatchException e) {
StdOut.println ("Input format error");
return null;
}
}
public static Person makePerson (String name, int age) {
return new Person (name, age);
}
static class Person {
String name;
int age;
public Person (String name, int age) {
this.name = name;
this.age = age;
}
public String toString () {
return name + " " + age;
}
// assuming name is always given in lower case
@Override
public boolean equals (Object obj) {
// TODO
if (obj instanceof Person) {
Person p = (Person) obj;
return this.name.equals(p.name) && this.age == p.age;
}
return false;
}
@Override
public int hashCode () {
// TODO
int result = this.age * 53;
for (char c : this.name.toCharArray()) {
result = (int) (result * c) / 13;
}
return result;
}
}
HashMap<Person,HashSet<Person>> map = new HashMap<>();
// a person "exists" after they are added using addPerson
// addPerson does nothing if p already exists
public void addPerson (Person p) {
// TODO
if (!map.containsKey(p)) {
map.put(p, new HashSet<Person>());
}
if (DEBUG) { StdOut.format ("P %s: %s ", p, map); }
}
// addFriendship does nothing if p1 and p2 are already friends or if one does not exist
public void addFriendship (Person p1, Person p2) {
// TODO
if (!p1.equals(p2) && map.containsKey(p1) && map.containsKey(p2) && !map.get(p1).contains(p2)) {
map.get(p1).add(p2);
map.get(p2).add(p1);
}
if (DEBUG) { StdOut.format ("F %s %s: %s ", p1, p2, map); }
}
// removeFriendship does nothing if p1 and p2 are not friends or if one does not exist
public void removeFriendship (Person p1, Person p2) {
// TODO
if (this.queryFriendship(p1, p2)) {
map.get(p1).remove(p2);
map.get(p2).remove(p1);
}
if (DEBUG) { StdOut.format ("U %s %s: %s ", p1, p2, map); }
}
// queryFriendship returns false if p1 and p2 are not friends or if one does not exist
public boolean queryFriendship (Person p1, Person p2) {
if (DEBUG) { StdOut.format ("Q %s %s: ", p1, p2); }
// TODO
return !p1.equals(p2) && map.containsKey(p1) && map.get(p1).contains(p2);
}
// lookupFriends returns null or empty iterable if p does not exists
public Iterable<Person> lookupFriends (Person p) {
if (DEBUG) { StdOut.format ("L %s:", p); }
// TODO
if (map.containsKey(p)) {
return (Iterable<Person>) map.get(p);
}
return null;
}
public static void hashTest () {
Trace.showBuiltInObjects (true);
//Trace.run ();
Person x = makePerson ("bob", 27);
Person y = makePerson ("bob", 27);
Boolean eq = x.equals(y);
Boolean hash = x.hashCode() == y.hashCode();
StdOut.println(x.toString() + " ("+x.hashCode()+") == " + y.toString() + " ("+y.hashCode()+")");
StdOut.println( " Equal Test: " + (eq ? "equal" : "not equal") );
StdOut.println( " Hash Test: " + (hash ? "equal" : "not equal") );
x = makePerson ("mike", 27);
y = makePerson ("john", 29);
eq = x.equals(y);
hash = x.hashCode() == y.hashCode();
StdOut.println(x.toString() + " ("+x.hashCode()+") == " + y.toString() + " ("+y.hashCode()+")");
StdOut.println( " Equal Test: " + (eq ? "equal" : "not equal") );
StdOut.println( " Hash Test: " + (hash ? "equal" : "not equal") );
}
public static void main (String[] args) {
Trace.showBuiltInObjects (true);
//Trace.run ();
hashTest();
/*
* The first line below causes "in" to read from the console. You can
* change this to read from a file, by using something like the line
* below, where "input.txt" is a file you create in your eclipse
* workspace. The file should be in the same folder that contains "src"
* "bin" and "lib":
*/
//In[] inputFiles = new In[] { new In () }; // from console
In[] inputFiles = new In[] { new In ("input.txt") }; // from file
//In[] inputFiles = new In[] { new In ("input.txt"), new In () }; // from file, then console
MyFB fb = new MyFB ();
StdOut.println (" ");
StdOut.println ("Enter one of the following:");
StdOut.println (" P name age -- add person");
StdOut.println (" F name1 age1 name2 age2 -- add friendship");
StdOut.println (" U name1 age1 name2 age2 -- remove friendship");
StdOut.println (" Q name1 age1 name2 age2 -- query friendship");
StdOut.println (" L name age -- lookup friends");
StdOut.println (" R -- restart");
StdOut.println (" X -- exit ");
for (In in : inputFiles) {
while (in.hasNextLine ()) {
String action;
try {
action = in.readString ();
} catch (NoSuchElementException e) { continue; }
//StdOut.println (action); // while debugging, print debugging info here! You can print maps, sets, lists.
switch (action) {
case "P":
case "p": {
Person p = makePerson (in);
fb.addPerson (p);
break;
}
case "F":
case "f": {
Person p1 = makePerson (in);
Person p2 = makePerson (in);
fb.addFriendship (p1, p2);
break;
}
case "U":
case "u": {
Person p1 = makePerson (in);
Person p2 = makePerson (in);
fb.removeFriendship (p1, p2);
//Trace.draw ();
break;
}
case "Q":
case "q": {
Person p1 = makePerson (in);
Person p2 = makePerson (in);
boolean result = fb.queryFriendship (p1, p2);
StdOut.println (result ? "Yes" : "No");
break;
}
case "L":
case "l": {
Person p = makePerson (in);
Iterable<Person> result = fb.lookupFriends (p);
if (result != null) {
for (Person friend : result) {
StdOut.print (friend);
StdOut.print (" ");
}
}
StdOut.println ();
break;
}
case "R":
case "r":
fb = new MyFB ();
break;
case "X":
case "x":
System.exit (0);
}
}
}
}
}
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