All 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].

Solution

dfs...注意判断是否相同

Complexity

时间复杂度 O(n!)

Code

public class Solution {
    public List<List<Integer>> permuteUnique(int[] num) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        List<Integer> path = new ArrayList<Integer>();
        Arrays.sort(num);
        boolean[] visited = new boolean[num.length];
        Arrays.fill(visited, false);
        permuteRe(num, res, path,visited);
        return res;
    }
    
    void permuteRe(int[] num, List<List<Integer>> res, List<Integer> path, boolean[] visited) {
        if(path.size() == num.length) {
            ArrayList<Integer> tmp = new ArrayList<Integer>(path);
            res.add(tmp);
            return;
        }
        for (int i = 0; i < num.length; ++i) {
            if(visited[i]||(i!=0&&num[i-1]==num[i]&&visited[i-1])) continue;
            visited[i] = true;
            path.add(num[i]);
            permuteRe(num, res, path, visited);
            path.remove(path.size() - 1);
            visited[i] = false;
        }
    }
}