Java Stream 排列组合

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使用 Java Stream 实现排列组合
  1 package org.htsg.utils;
  2 
  3 import java.util.ArrayList;
  4 import java.util.Arrays;
  5 import java.util.List;
  6 import java.util.stream.Collectors;
  7 import java.util.stream.IntStream;
  8 import java.util.stream.Stream;
  9 
 10 /**
 11  * @author HTSG
 12  */
 13 
 14     /**
 15      * 获取数组元素的全组合
 16      *
 17      * @param sources 源数组
 18      * @param <E>     类型
 19      * @return 全组合
 20      */
 21     public static <E> List<List<E>> combination(E[] sources) {
 22         return IntStream.range(1, 1 << sources.length)
 23                 .parallel()
 24                 .mapToObj(i -> IntStream.range(0, sources.length)
 25                         .filter(j -> (i & (1 << j)) != 0)
 26                         .mapToObj(j -> sources[j])
 27                         .collect(Collectors.toList()))
 28                 .collect(Collectors.toList());
 29     }
 30 
 31     public static <E> List<List<E>> combination(List<E> sources) {
 32         return IntStream.range(1, 1 << sources.size())
 33                 .parallel()
 34                 .mapToObj(i -> IntStream.range(0, sources.size())
 35                         .filter(j -> (i & (1 << j)) != 0)
 36                         .mapToObj(sources::get)
 37                         .collect(Collectors.toList()))
 38                 .collect(Collectors.toList());
 39     }
 40 
 41     /**
 42      * 获取数组元素的全排列
 43      *
 44      * @param sources 源数组
 45      * @param <E>     类型
 46      * @return 全排列
 47      */
 48     public static <E> List<List<E>> fullPermutationBySelf(E[] sources) {
 49         return fullPermutationBySelf(Arrays.asList(sources));
 50     }
 51 
 52     public static <E> List<List<E>> fullPermutationBySelf(List<E> sources) {
 53         Stream<List<E>> stream = sources.parallelStream().map(Arrays::asList);
 54         for (int i = 1; i < sources.size(); i++) {
 55             stream = stream
 56                     .flatMap(l ->
 57                             sources.stream()
 58                                     .filter(e -> !l.contains(e))
 59                                     .map(e -> {
 60                                         ArrayList<E> temp = new ArrayList<>(l);
 61                                         temp.add(e);
 62                                         return temp;
 63                                     }));
 64         }
 65         return stream.collect(Collectors.toList());
 66     }
 67 
 68     /**
 69      * 获取数组元素的排列
 70      *
 71      * @param sources 源数组
 72      * @param <E>     类型
 73      * @return 排列
 74      */
 75     public static <E> List<List<E>> permutationBySelf(E[] sources) {
 76         return permutationBySelf(Arrays.asList(sources));
 77     }
 78 
 79     public static <E> List<List<E>> permutationBySelf(List<E> sources) {
 80         Stream<List<E>> stream = sources.parallelStream().map(Arrays::asList);
 81         for (int i = 1; i < sources.size(); i++) {
 82             stream = stream
 83                     .flatMap(l ->
 84                             sources.stream()
 85                                     .map(e -> {
 86                                         ArrayList<E> temp = new ArrayList<>(l);
 87                                         temp.add(e);
 88                                         return temp;
 89                                     }));
 90         }
 91         return stream.collect(Collectors.toList());
 92     }
 93 
 94     public static <E> List<List<E>> permutation(List<List<E>> sources) {
 95         Stream<List<E>> stream = sources.get(0).stream().map(Arrays::asList);
 96         for (int i = 1; i < sources.size(); i++) {
 97             final int index = i;
 98             stream = stream.flatMap(l -> sources.get(index).stream()
 99                     .map(e -> {
100                         ArrayList<E> temp = new ArrayList<>(l);
101                         temp.add(e);
102                         return temp;
103                     }));
104         }
105         return stream.collect(Collectors.toList());
106     }
posted on 2022-07-04 10:02 河图书卦阅读(343) 评论(0) 收藏举报
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