java实现求一个项目集合任意元子集的通用算法

在关联规则挖掘过程中，经常涉及到求一个频繁项目集的n元子集，在此设计了一个通过位操作映射子集的通用算法。

import java.util.BitSet; import java.util.HashSet; import java.util.Iterator; import java.util.Set; public class FindSubset { private BitSet start; private BitSet end; private Set<Set<Object>> subsets; public FindSubset() { this.start = new BitSet(); this.end = new BitSet(); this.subsets = new HashSet<Set<Object>>(); } public void execute(int n, Set<Object> items) { int size = items.size(); for (int i = 0; i < n; i++) { start.set(i, true); } for (int i = n; i < size; i++) { start.set(i, false); } for (int i = size - 1; i > size - n; i--) { end.set(i, true); } for (int i = 0; i < size - n; i++) { end.set(i, false); } find(items); while (start != end) { boolean endBit = start.get(size - 1); int last10 = -1; int i; for (i = size - 1; i > 0; i--) { boolean former = start.get(i - 1); boolean last = start.get(i); if (former == true && last == false) { last10 = i - 1; break; } } if (i == 0) { break; } else { if (endBit == false) { start.set(last10, false); start.set(last10 + 1, true); find(items); } else { start.set(last10, false); start.set(last10 + 1, true); last10 += 1; for (int j = last10 + 1; j < size; j++) { if (start.get(j)) { start.set(j, false); start.set(last10 + 1, true); last10 += 1; find(items); } } } } } } public void find(Set<Object> items) { Set<Object> temp = new HashSet<Object>(); Object elements[] = items.toArray(); for (int i = 0; i < elements.length; i++) { if (start.get(i)) { temp.add(elements[i]); } } subsets.add(temp); } public Set<Set<Object>> getSubsets() { return this.subsets; } public void clearSubsets(){ this.subsets.clear(); } public static void main(String[] args) { Set<Object> items = new HashSet<Object>(); items.add("A"); items.add("B"); items.add("C"); items.add("D"); items.add("E"); items.add("F"); FindSubset fs = new FindSubset(); for (int i = 0; i < items.size(); i++) { System.out.println((i + 1) + "元子集："); fs.execute(i + 1, items); Iterator<Set<Object>> iterator = fs.getSubsets().iterator(); while (iterator.hasNext()) { Object[] subset = iterator.next().toArray(); System.out.print("{"); for (int j = 0; j < subset.length - 1; j++) { System.out.print(subset[j] + ","); } System.out.print(subset[subset.length - 1]); System.out.println("}"); } fs.clearSubsets(); } } }

测试结果：

1元子集： {D} {E} {F} {A} {B} {C} 2元子集： {D,E} {F,C} {E,C} {F,B} {E,F} {D,F} {A,B} {B,C} {D,A} {A,C} {D,C} {E,B} {F,A} {D,B} {E,A} 3元子集： {E,F,B} {D,F,C} {E,F,A} {D,F,B} {D,E,C} {D,E,F} {E,F,C} {F,A,B} {E,A,C} {D,B,C} {E,A,B} {D,A,C} {F,B,C} {D,F,A} {D,E,B} {F,A,C} {E,B,C} {D,E,A} {D,A,B} {A,B,C} 4元子集： {D,E,F,C} {D,E,F,B} {E,F,B,C} {D,E,F,A} {D,A,B,C} {E,A,B,C} {E,F,A,B} {D,F,A,C} {D,E,B,C} {E,F,A,C} {D,F,B,C} {F,A,B,C} {D,E,A,B} {D,F,A,B} {D,E,A,C} 5元子集： {D,E,F,B,C} {D,E,F,A,C} {D,E,F,A,B} {E,F,A,B,C} {D,F,A,B,C} {D,E,A,B,C} 6元子集： {D,E,F,A,B,C}