leetcode 47. 全排列 II(java)

java:

回溯 

class Solution {
    boolean[] vis;
    public List<List<Integer>> permuteUnique(int[] nums) {
        List<List<Integer>> ans = new ArrayList<>();
        List<Integer> list = new ArrayList<>();
        Arrays.sort(nums);
        vis = new boolean[nums.length];
        bt(nums, ans, list, 0);
        return ans;
    }
    public void bt(int[] nums, List<List<Integer>> ans, List<Integer> list, int flag){
        if(flag == nums.length){
            ans.add(new ArrayList<Integer>(list));
            return;
        }
        for(int i = 0; i < nums.length; i ++){
            if(vis[i] || (i > 0 && nums[i] == nums[i - 1] && !vis[i - 1])) continue;
            list.add(nums[i]);
            vis[i] = true;
            bt(nums, ans, list, flag + 1);
            vis[i] = false;
            list.remove(flag);
        }
    }
}