46. Permutations

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Problem

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

For example, [1,2,3] have the following permutations:

[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]

Constraints:

• 1 <= nums.length <= 6
• -10 <= nums[i] <= 10
• All the integers of nums are unique.

Code

class Solution {
    public List<List<Integer>> permute(int[] nums) {
        List<List<Integer>> list = new ArrayList<>();

        backtrack(list, new ArrayList<>(), nums);
        return list;
    }

    private void backtrack(List<List<Integer>> list,
                           List<Integer> tempList,
                           int [] nums){

        if(tempList.size() == nums.length){
            list.add(new ArrayList<>(tempList));
            return;
        }

        for(int i = 0; i < nums.length; i++){
            // 查看重复
            if(tempList.contains(nums[i])) continue;
            tempList.add(nums[i]);
            backtrack(list, tempList, nums);
            tempList.remove(tempList.size() - 1);
        }
    }
}