46. Permutations （backtracking）

[Shawngbk]

public class Solution { public List<List> permute(int[] nums) { List<List> res = new ArrayList<List>(); List list = new ArrayList(); helper(res, list, nums); return res; }

private void helper(List<List<Integer>> res, List<Integer> list, int[] nums) {
    for(int i = 0; i < nums.length; i++) {
        if(!list.contains(nums[i])) {
            list.add(nums[i]);
            if(list.size() == nums.length) {
                res.add(new ArrayList<Integer>(list));
            } else {
                helper(res, list, nums);
            }
            //每次删掉最后一个元素，能让每一个元素都出现在该位置上backtracking
            list.remove(list.size()-1);
        }
    }
}

}

[Shawngbk]

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