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WeightedQuickUnionUF.java
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WeightedQuickUnionUF.java
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public class WeightedQuickUnionUF {
private int[] parent; // parent[i] = parent of i
private int[] size; // size[i] = number of elements in subtree rooted at i
private int count; // number of components
public WeightedQuickUnionUF(int n) {
count = n;
parent = new int[n];
size = new int[n];
for (int i = 0; i < n; i++) {
parent[i] = i;
size[i] = 1;
}
}
public int count() {
return count;
}
public int find(int p) {
validate(p);
while (p != parent[p])
p = parent[p];
return p;
}
@Deprecated
public boolean connected(int p, int q) {
return find(p) == find(q);
}
// validate that p is a valid index
private void validate(int p) {
int n = parent.length;
if (p < 0 || p >= n) {
throw new IllegalArgumentException("index " + p + " is not between 0 and " + (n-1));
}
}
public void union(int p, int q) {
int rootP = find(p);
int rootQ = find(q);
if (rootP == rootQ) return;
// make smaller root point to larger one
if (size[rootP] < size[rootQ]) {
parent[rootP] = rootQ;
size[rootQ] += size[rootP];
}
else {
parent[rootQ] = rootP;
size[rootP] += size[rootQ];
}
count--;
}
public static void main(String[] args) {
int n = StdIn.readInt();
WeightedQuickUnionUF uf = new WeightedQuickUnionUF(n);
while (!StdIn.isEmpty()) {
int p = StdIn.readInt();
int q = StdIn.readInt();
if (uf.find(p) == uf.find(q)) continue;
uf.union(p, q);
StdOut.println(p + " " + q);
}
StdOut.println(uf.count() + " components");
}
}