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‎Assignment2/DisjointSets.java‎

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//created by Xingya Ren
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import java.io.*;
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import java.util.*;
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/****************************
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*
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* COMP251 template file
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*
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* Assignment 2, Question 1
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*
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*****************************/
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public class DisjointSets {
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private int[] par;
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private int[] rank;
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/* contructor: creates a partition of n elements. */
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/* Each element is in a separate disjoint set */
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DisjointSets(int n) {
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if (n>0) {
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par = new int[n];
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rank = new int[n];
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for (int i=0; i<this.par.length; i++) {
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par[i] = i;
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}
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}
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}
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public String toString(){
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int pari,countsets=0;
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String output = "";
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String[] setstrings = new String[this.par.length];
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/* build string for each set */
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for (int i=0; i<this.par.length; i++) {
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pari = find(i);
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if (setstrings[pari]==null) {
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setstrings[pari] = String.valueOf(i);
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countsets+=1;
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} else {
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setstrings[pari] += "," + i;
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}
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}
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/* print strings */
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output = countsets + " set(s):\n";
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for (int i=0; i<this.par.length; i++) {
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if (setstrings[i] != null) {
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output += i + " : " + setstrings[i] + "\n";
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}
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}
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return output;
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}
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/* find resentative of element i */
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public int find(int i) {
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/* Fill this method (The statement return 0 is here only to compile) */
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if(par[i]==i){
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//i's parent is itself --> self-loop
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return i;
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}else {
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int result = find(par[i]);
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par[i] = result;
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return result; //return the rep
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}
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}
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/* merge sets containing elements i and j */
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public int union(int i, int j) {
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/* Fill this method (The statement return 0 is here only to compile) */
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//get the ranks of i and j
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int iRep = this.find(i);
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int jRep = this.find(j);
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//if elements are in the same set, we do nothing and return the rep
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if(iRep==jRep) {
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return iRep;
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}
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//get the ranks
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int iRank = 0;
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int jRank = 0;
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iRank = rank[iRep];
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jRank = rank[jRep];
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//compare the ranks to see who should be the new parent
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if(iRank == jRank) {
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//merge i into j
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this.par[iRep] = jRep;
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rank[jRep]++; //increment the rank by one
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return jRep;
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}else if(iRank < jRank) {
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//merge i into j
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this.par[iRep] = jRep;
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return jRep;
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}else {
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//merge j into i
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this.par[jRep] = iRep;
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return iRep;
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}
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}
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public static void main(String[] args) {
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DisjointSets myset = new DisjointSets(6);
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System.out.println(myset);
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System.out.println("-> Union 2 and 3");
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myset.union(2,3);
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System.out.println(myset);
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System.out.println("-> Union 2 and 3");
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myset.union(2,3);
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System.out.println(myset);
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System.out.println("-> Union 2 and 1");
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myset.union(2,1);
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System.out.println(myset);
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System.out.println("-> Union 4 and 5");
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myset.union(4,5);
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System.out.println(myset);
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System.out.println("-> Union 3 and 1");
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myset.union(3,1);
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System.out.println(myset);
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System.out.println("-> Union 2 and 4");
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myset.union(2,4);
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System.out.println(myset);
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}
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}

‎Assignment2/HW_Sched.java‎

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//created by Xingya Ren
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import java.util.*;
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class Assignment implements Comparator<Assignment>{
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int number;
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int weight;
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int deadline;
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protected Assignment() {
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}
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protected Assignment(int number, int weight, int deadline) {
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this.number = number;
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this.weight = weight;
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this.deadline = deadline;
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}
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/**
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* This method is used to sort to compare assignment objects for sorting.
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* Return -1 if a1 > a2
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* Return 1 if a1 < a2
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* Return 0 if a1 = a2
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*/
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@Override
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public int compare(Assignment a1, Assignment a2) {
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// TODO Implement this
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//sort by weight in descending order
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//if there is a tie-->put the one that has larger deadline before
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if(a1.weight < a2.weight) {
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return 1;
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}else if(a1.weight > a2.weight) {
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return -1;
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}else {
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//two have the same weights
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//the one with larger deadline comes first
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if(a1.deadline < a2.deadline) {
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return 1;
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}else {
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return -1;
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}
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}
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}
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}
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public class HW_Sched {
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ArrayList<Assignment> Assignments = new ArrayList<Assignment>();
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int m;
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int lastDeadline = 0;
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protected HW_Sched(int[] weights, int[] deadlines, int size) {
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for (int i=0; i<size; i++) {
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Assignment homework = new Assignment(i, weights[i], deadlines[i]);
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this.Assignments.add(homework);
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if (homework.deadline > lastDeadline) {
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lastDeadline = homework.deadline;
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}
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}
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m =size;
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}
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/**
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*
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* @return Array where output[i] corresponds to the assignment
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* that will be done at time i.
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*/
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public int[] SelectAssignments() {
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//TODO Implement this
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//Sort assignments
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//Order will depend on how compare function is implemented
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Collections.sort(Assignments, new Assignment());
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// If schedule[i] has a value -1, it indicates that the
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// i'th timeslot in the schedule is empty
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int[] homeworkPlan = new int[lastDeadline];
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for (int i=0; i < homeworkPlan.length; ++i) {
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homeworkPlan[i] = -1;
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}
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//STUDENT CODE STARTS HERE
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//add assign to the array
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//if the next one should come before, then swap(?)
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//loop through the sorted list
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//get the largest deadline
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//check if that corresponding slot is occupied
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//if it is -->go to the previous slot
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//if not --> assign the assignment
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for(int i=1; i<=Assignments.size(); i++) {
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int theDdl = Assignments.get(i-1).deadline;
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if(homeworkPlan[theDdl-1] == -1) {
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//there is currently no assignment assiged to this slot
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homeworkPlan[theDdl-1] = Assignments.get(i-1).number;
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}else {
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//go to the previous slot
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for(int j=theDdl-2; j>=0; j--) {
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if (homeworkPlan[j]==-1) {
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homeworkPlan[j] = Assignments.get(i-1).number;
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break;
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}
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}
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}
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}
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return homeworkPlan;
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}
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}
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‎Assignment2/Kruskal.java‎

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//created by Xingya Ren
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import java.util.*;
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public class Kruskal{
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public static WGraph kruskal(WGraph g){
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/* Fill this method (The statement return null is here only to compile) */
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//takes a graph as input and returns a new graph object that is the MST of the given graph
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//sort the list of nodes in ascending weights
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WGraph minSpanTree = new WGraph();
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DisjointSets setForTheGraph = new DisjointSets(g.getNbNodes()); //because we can't do union on a graph we turn it into a set
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//loop through the list of sorted edges
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for(Edge e: g.listOfEdgesSorted()) {
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if(IsSafe(setForTheGraph, e)) {
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//is safe to add --> add it
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minSpanTree.addEdge(e);
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setForTheGraph.union(e.nodes[0], e.nodes[1]);
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}
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}
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return minSpanTree;
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}
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public static Boolean IsSafe(DisjointSets p, Edge e){
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/* Fill this method (The statement return 0 is here only to compile) */
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//nodes p; edge e
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//returns true if it is safe to add the edge e to this graph
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//false if not
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//Using DisjointSets from the previous question
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//DisjointSets has: int find(int i) which returns the representative
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// int union(int i, int j) which merges two sets and return the rep
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//sort the nodes in ascending order
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//an array list that holds the sorted edges
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int node1 = e.nodes[0];
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int node2 = e.nodes[1];
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int node1Rep, node2Rep;
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node1Rep = p.find(node1);
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node2Rep = p.find(node2);
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if(node1Rep == node2Rep) {
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//in the same set --> not safe
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return false;
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}else{
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return true; //different rep's --> different sets
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}
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}
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public static void main(String[] args){
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String file = args[0];
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WGraph g = new WGraph(file);
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WGraph t = kruskal(g);
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System.out.println(t);
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}
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}

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