Permutations

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Given a list of numbers, return all possible permutations.

class Solution {    /**     * @param nums: A list of integers.     * @return: A list of permutations.     */    public List<List<Integer>> permute(int[] nums) {        List<List<Integer>> results = new ArrayList<>();        if (nums == null) {            return results;        }        if (nums.length == 0) {            results.add(new ArrayList<Integer>());            return results;        }        List<Integer> result = new ArrayList<>();        dfsHelper(nums, results, result);        return results;    }    private void dfsHelper(int[] nums,                           List<List<Integer>> results,                           List<Integer> result) {        if (result.size() == nums.length) {            results.add(new ArrayList<Integer>(result));        }        for (int i = 0; i < nums.length; i++) {            if (result.contains(nums[i])) {                continue;            }            result.add(nums[i]);            dfsHelper(nums, results, result);            result.remove(result.size() - 1);        }    }}

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