(UVA) Claw Decomposition - Solution
Link to the problem: https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=669&page=show_problem&problem=2391
For this problem, we need to find out if the graph is bipartite. The solution below used a Breath-First Search (BFS) to accomplish this task.
import java.io.*;
import java.util.*;
class Main {
public ArrayList<ArrayList<Integer>> adjList;
public int[] nodes;
public boolean bfs(int start, int numNodes) {
Queue<Integer> queue = new ArrayDeque<>();
queue.add(start);
nodes[start] = 0;
while (queue.size() > 0) {
int currNode = queue.poll();
ArrayList<Integer> reachNodes = adjList.get(currNode);
for (int i = 0; i < reachNodes.size(); i++) {
if (nodes[reachNodes.get(i)] == -1) { // not visited yet
nodes[reachNodes.get(i)] = (nodes[currNode]+1)%2;
queue.add(reachNodes.get(i));
}
else if (nodes[reachNodes.get(i)] == nodes[currNode]) {
return false;
}
}
}
return true;
}
public void process() throws NumberFormatException, IOException {
Scanner sc = new Scanner(System.in);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
int numNodes = sc.nextInt();
while (numNodes != 0) {
adjList = new ArrayList<>();
for (int i = 0; i <= numNodes; i++) {
adjList.add(new ArrayList<Integer>());
}
int n1 = sc.nextInt();
int n2 = sc.nextInt();
while (n1 != 0 || n2 != 0) {
adjList.get(n1).add(n2);
adjList.get(n2).add(n1);
n1 = sc.nextInt();
n2 = sc.nextInt();
}
nodes = new int[numNodes+1];
for (int i = 0; i <= numNodes; i++) {
nodes[i] = -1;
}
boolean b = bfs(1, numNodes);
String s = b ? "YES" : "NO";
bw.write(s+"\n");
numNodes = sc.nextInt();
}
bw.flush();
bw.close();
return;
}
public static void main(String[] args) throws NumberFormatException, IOException {
Main m = new Main();
m.process();
System.exit(0);
}
}
For this problem, we need to find out if the graph is bipartite. The solution below used a Breath-First Search (BFS) to accomplish this task.
import java.io.*;
import java.util.*;
class Main {
public ArrayList<ArrayList<Integer>> adjList;
public int[] nodes;
public boolean bfs(int start, int numNodes) {
Queue<Integer> queue = new ArrayDeque<>();
queue.add(start);
nodes[start] = 0;
while (queue.size() > 0) {
int currNode = queue.poll();
ArrayList<Integer> reachNodes = adjList.get(currNode);
for (int i = 0; i < reachNodes.size(); i++) {
if (nodes[reachNodes.get(i)] == -1) { // not visited yet
nodes[reachNodes.get(i)] = (nodes[currNode]+1)%2;
queue.add(reachNodes.get(i));
}
else if (nodes[reachNodes.get(i)] == nodes[currNode]) {
return false;
}
}
}
return true;
}
public void process() throws NumberFormatException, IOException {
Scanner sc = new Scanner(System.in);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
int numNodes = sc.nextInt();
while (numNodes != 0) {
adjList = new ArrayList<>();
for (int i = 0; i <= numNodes; i++) {
adjList.add(new ArrayList<Integer>());
}
int n1 = sc.nextInt();
int n2 = sc.nextInt();
while (n1 != 0 || n2 != 0) {
adjList.get(n1).add(n2);
adjList.get(n2).add(n1);
n1 = sc.nextInt();
n2 = sc.nextInt();
}
nodes = new int[numNodes+1];
for (int i = 0; i <= numNodes; i++) {
nodes[i] = -1;
}
boolean b = bfs(1, numNodes);
String s = b ? "YES" : "NO";
bw.write(s+"\n");
numNodes = sc.nextInt();
}
bw.flush();
bw.close();
return;
}
public static void main(String[] args) throws NumberFormatException, IOException {
Main m = new Main();
m.process();
System.exit(0);
}
}
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