并查集
并查集是重要的数据结构，在算法编写中很常见。
这里写的比较平实，不使用联合启发式或路径压缩算法。
集合中的元素从0开始编号。
可结合着看：并查集V1.0——森林版。
核心功能
- void union(root1, root2) → Merge two sets
- int find(x) → Return set containing x
编程实现
/**
* Disjoint set class.
* Does not use union heuristics or path compression.
* Elements in the set are numbered starting at 0.
*/
class DisjSetsSlow {
private int[] set;
/**
* Construct the disjoint sets object.
* @param numElements the initial number of disjoint sets.
*/
public DisjSetsSlow(int numElements) {
set = new int [numElements];
for(int i = 0; i < set.length; i++) {
set[i] = -1;
}
}
/**
* Union two disjoint sets.
* For simplicity, we assume root1 and root2 are distinct
* and represent set names.
* @param root1 the root of set 1.
* @param root2 the root of set 2.
*/
public void union(int root1, int root2) {
set[root2] = root1;
}
/**
* Perform a find.
* Error checks omitted again for simplicity.
* @param x the element being searched for.
* @return the set containing x.
*/
public int find(int x) {
if(set[x] < 0) {
return x;
} else {
return find(set[x]);
}
}
}
测试
public class DisjSetsSlowTest {
public static void main(String [] args) {
int NumElements = 128;
int NumInSameSet = 16;
DisjSetsSlow ds = new DisjSetsSlow(NumElements);
int set1, set2;
for(int k = 1; k < NumInSameSet; k *= 2) {
for(int j = 0; j + k < NumElements; j += 2 * k) {
set1 = ds.find(j);
set2 = ds.find(j + k);
ds.union(set1, set2);
}
}
StringBuilder tempResult = new StringBuilder();
for(int i = 0; i < NumElements; i++) {
tempResult.append(ds.find(i)).append("~");
if(i % NumInSameSet == NumInSameSet-1) {
System.out.println(tempResult.substring(0, tempResult.length()-1));
tempResult = new StringBuilder();
}
}
}
}
测试结果：
0~0~0~0~0~0~0~0~0~0~0~0~0~0~0~0
16~16~16~16~16~16~16~16~16~16~16~16~16~16~16~16
32~32~32~32~32~32~32~32~32~32~32~32~32~32~32~32
48~48~48~48~48~48~48~48~48~48~48~48~48~48~48~48
64~64~64~64~64~64~64~64~64~64~64~64~64~64~64~64
80~80~80~80~80~80~80~80~80~80~80~80~80~80~80~80
96~96~96~96~96~96~96~96~96~96~96~96~96~96~96~96
112~112~112~112~112~112~112~112~112~112~112~112~112~112~112~112
