LeetCode刷题【47】全排列 II

给定一个可包含重复数字的序列 nums ，按任意顺序 返回所有不重复的全排列。

示例 1：

输入：nums = [1,1,2]
输出：
[[1,1,2],
 [1,2,1],
 [2,1,1]]

示例 2：

输入：nums = [1,2,3]
输出：[[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

提示：

• 1 <= nums.length <= 8
• -10 <= nums[i] <= 10

题解

回溯，同LeetCode刷题【剑指 Offer 38】字符串的排列

代码

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;

//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    List<List<Integer>> res;
    int[] nums;
    HashSet<Integer> samIndex;
    public List<List<Integer>> permuteUnique(int[] nums) {
        res = new ArrayList<>();
        samIndex = new HashSet<>();
        this.nums = nums;
        dfs(new ArrayList<>());
        return res;
    }


    private void dfs(List<Integer> list){
        if (list.size()==nums.length){
            res.add(new ArrayList<>(list));
            return;
        }
        HashSet<Integer> sameNum = new HashSet<>();
        for (int i = 0; i < nums.length; i++) {
            if (samIndex.contains(i)){
                continue;
            }
            int num = nums[i];
            if (sameNum.contains(num)) {
                continue;
            }
            samIndex.add(i);
            sameNum.add(num);
            list.add(num);
            dfs(list);
            samIndex.remove(i);
            list.remove(list.size() - 1);
        }
    }
}
//leetcode submit region end(Prohibit modification and deletion)