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UnionFind.java
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UnionFind.java
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package Graph;
/**
* @author kalpak
*
* Implement the Union Find algorithm with Path Compression.
*
* Inspired from William Fiset.
*
*/
public class UnionFind {
private int numberOfElements; // number of elements in union find
private int[] size; // track size of each component
private int[] id; // id[i] points to the parent of i, if id[i] = i, then i is the root node.
private int numOfComponents;
public UnionFind(int size) {
if(size <= 0)
throw new IllegalArgumentException("Size <= 0 is not allowed.");
this.numberOfElements = numOfComponents = size;
this.size = new int[size];
this.id = new int[size];
// Initialize the arrays as individual components
for(int i = 0; i < size; i++) {
id[i] = i; // self root
this.size[i] = 1;
}
}
public int find(int p) {
// find the root of the component
int root = p;
while(root != id[root])
root = id[root];
// Path Compression : Gives amortized time complexity
while(p != root) {
int next = id[p]; // Store the id of p and make p point to the root
id[p] = root; // Compress
p = next; // do the same for the rest.
}
return root;
}
public boolean isConnected(int p, int q) {
return find(p) == find(q);
}
public int componentSize(int p) {
return size[find(p)];
}
public int getNumberOfElements() {
return numberOfElements;
}
public int getNumOfComponents() {
return numOfComponents;
}
public void union(int p, int q) {
if(isConnected(p, q))
return;
int root1 = find(p);
int root2 = find(q);
// Merge component with smaller size to the component with larger size.
if(size[root1] < size[root2]) {
size[root2] += size[root1];
id[root1] = root2; // Merge
} else {
size[root1] += size[root2];
id[root2] = root1;
}
numOfComponents--;
}
}