Leetcode-Permutations

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].

Have you met this question in a real interview?
 
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 }

 

posted @ 2014-11-21 00:53  LiBlog  阅读(134)  评论(0)  编辑  收藏  举报