如何實現通過一個集合來生成有序項集的所有組合
阿新 • • 發佈:2018-12-08
import java.util.*; public class Combination { public static <T extends Comparable<? super T>> List<List<T>> findSortedCombinations(Collection<T> elements, int n){ List<List<T>> result = new ArrayList<List<T>>(); if(n == 0){ result.add(new ArrayList<T>()); return result; } List<List<T>> combinations = findSortedCombinations(elements, n - 1); System.out.println("回的次數"); for(List<T> combination : combinations){ System.out.println("combination\t"+combination); for(T element : elements){ System.out.println(element); if(combination.contains(element)){ System.out.println("combination包含了"+element+"\t"+combination); continue; } List<T> list = new ArrayList<T>(); list.addAll(combination); if(list.contains(element)){ System.out.println("list包含了"+element); continue; } list.add(element); Collections.sort(list); if(result.contains(list)){ System.out.println("result包含了"+list+"\t"+result); continue; } result.add(list); System.out.println(list+"\t\t"+result); } } return result; } public static <T extends Comparable<? super T>> List<List<T>> findSortedCombinations(Collection<T> elements){ List<List<T>> result = new ArrayList<List<T>>(); for(int i = 0; i <= elements.size(); i++){ result.addAll(findSortedCombinations(elements,i)); } return result; } public static void main(String[] args) { List<String> list = Arrays.asList("a", "b", "c", "d"); System.out.println("list="+ list); List<List<String>> comb = findSortedCombinations(list, 2); System.out.println(comb.size()); System.out.println(comb); } }