算法（Algorithms）第4版 练习 1.5.13

package com.qiusongde;

import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;

public class UFWQuickUnionPathCom {

private int[] id;//parent link(site indexed)
private int[] treesize;//size of component for roots(site indexed)
private int count;//number of components

public UFWQuickUnionPathCom(int N) {

count = N;

id = new int
;
for(int i = 0; i < N; i++)
id[i] = i;

treesize = new int
;
for(int i = 0; i < N; i++)
treesize[i] = 1;

}

public int count() {
return count;
}

public boolean connected(int p, int q) {
return find(p) == find(q);
}

public int find(int p) {

int root = p;//initialize root

//find root(id[p] save the parent of p)
while(root != id[root])
root = id[root];

//link every site from p to root to root
while(id[p] != root) {//parent isn't root
int nextp = id[p];
id[p] = root;//link directly to root
p = nextp;
}

return root;

}

public void union(int p, int q) {

int pRoot = find(p);
int qRoot = find(q);

if(pRoot == qRoot)
return;

//make smaller root point to larger one
if(treesize[pRoot] < treesize[qRoot]) {
id[pRoot] = qRoot;
treesize[qRoot] += treesize[pRoot];
} else {
id[qRoot] = pRoot;
treesize[pRoot] += treesize[qRoot];
}

count--;

}

@Override
public String toString() {
String s = "";

for(int i = 0; i < id.length; i++) {
s += id[i] + " ";
}
s += "\n";

for(int i = 0; i < treesize.length; i++) {
s += treesize[i] + " ";
}
s += "\n" + count + " components";

return s;
}

public static void main(String[] args) {

//initialize N components
int N = StdIn.readInt();
UFWQuickUnionPathCom uf = new UFWQuickUnionPathCom(N);
StdOut.println(uf);

while(!StdIn.isEmpty()) {

int p = StdIn.readInt();
int q = StdIn.readInt();

if(uf.connected(p, q)) {//ignore if connected
StdOut.println(p + " " + q + " is connected");
StdOut.println(uf);
continue;
}

uf.union(p, q);//connect p and q
StdOut.println(p + " " + q);
StdOut.println(uf);
}

}

}

0 1 2 3 4 5 6 7 8 9
1 1 1 1 1 1 1 1 1 1
10 components
4 3
0 1 2 4 4 5 6 7 8 9
1 1 1 1 2 1 1 1 1 1
9 components
3 8
0 1 2 4 4 5 6 7 4 9
1 1 1 1 3 1 1 1 1 1
8 components
6 5
0 1 2 4 4 6 6 7 4 9
1 1 1 1 3 1 2 1 1 1
7 components
9 4
0 1 2 4 4 6 6 7 4 4
1 1 1 1 4 1 2 1 1 1
6 components
2 1
0 2 2 4 4 6 6 7 4 4
1 1 2 1 4 1 2 1 1 1
5 components
8 9 is connected
0 2 2 4 4 6 6 7 4 4
1 1 2 1 4 1 2 1 1 1
5 components
5 0
6 2 2 4 4 6 6 7 4 4
1 1 2 1 4 1 3 1 1 1
4 components
7 2
6 2 2 4 4 6 6 2 4 4
1 1 3 1 4 1 3 1 1 1
3 components
6 1
6 2 6 4 4 6 6 2 4 4
1 1 3 1 4 1 6 1 1 1
2 components
1 0 is connected
6 6 6 4 4 6 6 2 4 4
1 1 3 1 4 1 6 1 1 1
2 components
6 7 is connected
6 6 6 4 4 6 6 6 4 4
1 1 3 1 4 1 6 1 1 1
2 components