47. 全排列 II

给定一个可包含重复数字的序列，返回所有不重复的全排列。

示例:

输入: [1,1,2]

输出:

[

[1,1,2],

[1,2,1],

[2,1,1]

]

class Solution {

    List<List<Integer>> ans = new ArrayList<>();

    public List<List<Integer>> permuteUnique(int[] nums) {

        dfs(nums,0);

        return ans;

    }

    private void dfs(int[] nums,int cur) {

        if (cur == nums.length) {

            List<Integer> line = new ArrayList<>();

            for (int i : nums) {

                line.add(i);

            }

            ans.add(line);

        } else {

            for (int i = cur;i < nums.length;i++) {

                if (canSwap(nums,cur,i)) {

                    swap(nums,cur,i);

                    dfs(nums,cur + 1);

                    swap(nums,cur,i);

                }

            }

        }

    }

    private boolean canSwap(int nums[],int begin,int end) {

        for (int i = begin;i < end;i++) {

            if (nums[i] == nums[end]) {

                return false;

            }

        }

        return true;

    }

    private void swap(int nums[],int i,int j) {

        int temp = nums[i];

        nums[i] = nums[j];

        nums[j] = temp;

    }

}