LeetCode_47---Permutations II

Given a collection of numbers that might contain duplicates, return all possible unique permutations.
For example,

[1,1,2]

 have the following unique permutations:

[1,1,2]

, 

[1,2,1]

,
and 

[2,1,1]

.

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 Backtracking

Code:

/**
*
*/
package From41;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;

/**
* @author MohnSnow
* @time 2015年6月24日 下午2:15:16
*
*/
public class LeetCode47 {

/**
* @param argsmengdx
* -fnst
*/
public static List<List<Integer>> permuteUnique(int[] nums) {
List<List<Integer>> result = new LinkedList<List<Integer>>();
if (nums == null || nums.length == 0) {
List<Integer> temp = new ArrayList<Integer>();
result.add(temp);
return result;
}
Arrays.sort(nums);
permute(result, nums, 0);
return result;
}

public static void permute(List<List<Integer>> result, int[] nums, int start) {
if (start == nums.length - 1) {
List<Integer> temp = new ArrayList<Integer>();
for (int j = 0; j < nums.length; j++) {
temp.add(nums[j]);
}
result.add(temp);
return;
}
for (int i = start; i < nums.length; i++) {
int temp;
if (i > start && nums[i] == nums[i - 1]) {
continue;
}
temp = nums[start];
nums[start] = nums[i];
nums[i] = temp;
permute(result, nums, start + 1);
temp = nums[start];
nums[start] = nums[i];
nums[i] = temp;
}
}

//340msAC---http://www.programcreek.com/2013/02/leetcode-permutations-ii-java/
//递归的Set去重算法会超时
public static List<List<Integer>> permuteUnique1(int[] nums) {
List<List<Integer>> returnList = new ArrayList<List<Integer>>();
returnList.add(new ArrayList<Integer>());
for (int i = 0; i < nums.length; i++) {
Set<ArrayList<Integer>> currentSet = new HashSet<ArrayList<Integer>>();
for (List<Integer> l : returnList) {
for (int j = 0; j < l.size() + 1; j++) {
l.add(j, nums[i]);
ArrayList<Integer> T = new ArrayList<Integer>(l);
l.remove(j);
currentSet.add(T);
}
}
returnList = new ArrayList<List<Integer>>(currentSet);
}
return returnList;
}

public static void main(String[] args) {
//int[] nums = { 3, 3, 0, 0 };
int[] nums = { 3, 3, 0, 0 };
System.out.println("排列s: " + permuteUnique(nums).toString());
System.out.println("排列s: " + permuteUnique1(nums).toString());
}

}