回溯法-求全排列

回溯法入门，求一个集合的全排列，比如{2,3,5}的全排列为：[[2, 3, 5], [2, 5, 3], [3, 2, 5], [3, 5, 2], [5, 3, 2], [5, 2, 3]]

代码如下：

public class AllPermutations {public void allPermutations(List<List<Integer>> lists, Integer[] a, int cur) {if (cur == a.length) {lists.add(new ArrayList<>(Arrays.asList(a)));} else {for (int i = cur; i < a.length; i++) {swap(a, cur, i);allPermutations(lists, a, cur+1);swap(a, cur, i);}}}public void swap(Integer[] a, int i, int j) {if (i == j) {return;}a[i] ^= a[j];a[j] ^= a[i];a[i] ^= a[j];}public static void main(String[] args) {AllPermutations ap = new AllPermutations();Integer[] a = {2, 3, 5};List<List<Integer>> lists = new ArrayList<>();ap.allPermutations(lists, a, 0);System.out.println(lists);System.out.println(lists.size());}