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-rw-r--r--src/ch/epfl/xblast/Lists.java35
1 files changed, 30 insertions, 5 deletions
diff --git a/src/ch/epfl/xblast/Lists.java b/src/ch/epfl/xblast/Lists.java
index f541b37..4ea45c2 100644
--- a/src/ch/epfl/xblast/Lists.java
+++ b/src/ch/epfl/xblast/Lists.java
@@ -1,8 +1,6 @@
1package ch.epfl.xblast; 1package ch.epfl.xblast;
2 2
3import java.util.ArrayList; 3import java.util.*;
4import java.util.Collections;
5import java.util.List;
6import java.util.stream.Collectors; 4import java.util.stream.Collectors;
7import java.util.stream.Stream; 5import java.util.stream.Stream;
8 6
@@ -45,12 +43,39 @@ public final class Lists {
45 } 43 }
46 44
47 /** 45 /**
46 * Returns a copy of the given list with element e inserted at index i.
47 *
48 * @param l the list
49 * @param i the insertion index
50 * @param e the element to insert
51 * @param <T> the type of the list's elements
52 * @return a copy of the list with the element inserted
53 */
54 public static <T> List<T> inserted(List<T> l, int i, T e) {
55 List<T> r = new LinkedList<>(l);
56 r.add(i, e);
57 return r;
58 }
59
60 /**
48 * Returns all the permutations of the elements of the given list 61 * Returns all the permutations of the elements of the given list
49 * 62 *
50 * @param l given list 63 * @param l given list
64 * @param <T> the type of the list's elements
51 * @return a list of all the permutations of the list 65 * @return a list of all the permutations of the list
66 * @throws IllegalArgumentException if the given list is null
52 */ 67 */
53 public static <T> List<List<T>> permutations(List<T> l) { 68 public static <T> List<List<T>> permutations(List<T> l) {
54 return null; 69 if (l == null) throw new IllegalArgumentException();
70 if (l.size() <= 1) return Collections.singletonList(l);
71 if (l.size() == 2) return Arrays.asList(l, Lists.reversed(l));
72
73 List<List<T>> p = new LinkedList<>();
74 for (List<T> sp : Lists.permutations(l.subList(1, l.size())))
75 for (int i = 0; i <= sp.size(); ++i)
76 p.add(Lists.inserted(sp, i, l.get(0)));
77
78 return p;
55 } 79 }
80
56} 81}