Medium
准备联系这个系列A general approach to backtracking questions in Java (Subsets, Permutations, Combination Sum, Palindrome Partioning)
简单，straightforward，没什么好说的
public class Solution {
public List<List<Integer>> permute(int[] nums) {
List<List<Integer>> res = new ArrayList<>();
if (nums == null || nums.length == 0){
return res;
}
List<Integer> list = new ArrayList<>();
dfsHelper(res, list, nums);
return res;
}
private void dfsHelper(List<List<Integer>> res, List<Integer> list, int[] nums){
if (list.size() == nums.length){
res.add(new ArrayList<Integer>(list));
return;
}
for (int i = 0; i < nums.length; i++){
if (list.contains(nums[i])){
continue;
}
list.add(nums[i]);
dfsHelper(res, list, nums);
list.remove(list.size() - 1);
}
}
}
