Given a collection of numbers, return all possible permutations.
For example,
[1,2,3] have the following permutations:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].
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Solution:
Use recursive method. This solution is a iterative recursive solution.
1 public class Solution { 2 public List<List<Integer>> permute(int[] num) { 3 int len = num.length; 4 List<List<Integer>> resSet = new ArrayList<List<Integer>>(); 5 List<Integer> curSeq = new ArrayList<Integer>(); 6 boolean[] used = new boolean[len]; 7 Arrays.fill(used,false); 8 Arrays.sort(num); 9 int curIndex = 0; 10 curSeq.add(-1); 11 while (curIndex!=-1){ 12 if (curIndex==len){ 13 List<Integer> temp = new ArrayList<Integer>(); 14 for (int i=0;i<curSeq.size();i++) temp.add(num[curSeq.get(i)]); 15 resSet.add(temp); 16 curIndex--; 17 continue; 18 } 19 20 int val = -1; 21 if (curSeq.size()>curIndex){ 22 val = curSeq.get(curIndex); 23 if (val!=-1) 24 used[val]=false; 25 curSeq.remove(curIndex); 26 } 27 28 boolean find = false; 29 for (int i=val+1;i<len;i++) 30 if (!used[i]){ 31 used[i]=true; 32 curSeq.add(i); 33 curIndex++; 34 find = true; 35 break; 36 } 37 38 if (find) 39 continue; 40 else 41 curIndex--; 42 } 43 44 return resSet; 45 } 46 }