46. Permutations(Medium)(dfs)

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/NCUscienceZ/article/details/86996102

Given a collection of distinct integers, return all possible permutations.

Example:

Input: [1,2,3]
Output:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]

dfs

class Solution {
    public List<List<Integer>> permute(int[] nums) {
        List<List<Integer>> ans = new LinkedList<>();
        Set<Integer> set = new HashSet<>();
        Arrays.sort(nums);
        dfs(ans, new LinkedList<Integer>(), set, nums, nums.length);
        return ans;
    }
    
    public void dfs(List<List<Integer>> ans, List<Integer> list, Set<Integer> set, int[] candidates, int target){
        if (target == 0){
            //ans.add(list);   又犯错误
            ans.add(new LinkedList<Integer>(list));
            return;
        }else{
            for (int i = 0; i<candidates.length; i++){
                if (set.contains(candidates[i])) continue;
                list.add(candidates[i]);
                set.add(candidates[i]);
                dfs(ans, list, set, candidates, target-1);
                set.remove(candidates[i]);
                list.remove(list.size()-1);
            }
        }
    }
}