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next permutation for Java List.
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| import java.util.Collections; | |
| import java.util.Comparator; | |
| import java.util.List; | |
| public class Permutations { | |
| /** | |
| * Rearrange the list into the next lexicographically greater permutation if exists. | |
| * | |
| * @return true if such a permutation exists, otherwise false. | |
| */ | |
| public static <T extends Comparable> boolean nextPermutation(List<T> list) { | |
| return nextPermutation(list, (a, b) -> a.compareTo(b)); | |
| } | |
| /** | |
| * Rearrange the list into the next lexicographically greater permutation if exists. | |
| * | |
| * @return true if such a permutation exists, otherwise false. | |
| */ | |
| public static <T> boolean nextPermutation(List<T> list, Comparator<T> comparator) { | |
| // Find the biggest i which meets list[i] < list[i + 1] | |
| int i = list.size() - 2; | |
| for (; i >= 0; i--) { | |
| T next = list.get(i + 1); | |
| T tmp = list.get(i); | |
| if (comparator.compare(tmp, next) < 0) { | |
| break; | |
| } | |
| } | |
| if (i < 0) { | |
| return false; | |
| } | |
| T pivot = list.get(i); | |
| // Find the biggest j where list[j - 1] > list[i]. | |
| int j = i + 2; | |
| for (; j < list.size(); j++) { | |
| if (comparator.compare(list.get(j), pivot) <= 0) break; | |
| } | |
| Collections.swap(list, i, j - 1); | |
| Collections.reverse(list.subList(i + 1, list.size())); | |
| return true; | |
| } | |
| } |
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