[leetcode]47. Permutations全排列(给定序列有重复元素)

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

Example:

Input: [1,1,2]
Output:
[
  [1,1,2],
  [1,2,1],
  [2,1,1]
]

题意：

打印全排列，注明了给定序列可含有重复元素

Solution1: Backtracking

code

 class Solution {
      public List<List<Integer>> permuteUnique(int[] nums) {
         List<List<Integer>> list = new ArrayList<>();
          List<Integer> path = new ArrayList<>();
         Arrays.sort(nums); // necessary！因为后面要查重
         dfs(list, path, nums, new boolean[nums.length]);
         return list;
 }

     private void dfs(List<List<Integer>> list, List<Integer> path, int [] nums, boolean [] used){
         if(path.size() == nums.length){
             list.add(new ArrayList<>(path));
             return;
         }
         for(int i = 0; i < nums.length; i++){
             if(used[i] || i > 0 && nums[i] == nums[i-1] && !used[i - 1]) continue;
             used[i] = true; //标记用过
             path.add(nums[i]);
             dfs(list, path, nums, used);
             used[i] = false; //恢复default值
             path.remove(path.size() - 1);
         }
     }
 }