Permutations

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Permutations

Given a list of numbers, return all possible permutations.

Example

For nums [1,2,3], the permutaions are:

[

[1,2,3],

[1,3,2],

[2,1,3],

[2,3,1],

[3,1,2],

[3,2,1]

]

Solution:

    public ArrayList<ArrayList<Integer>> permute(ArrayList<Integer> nums) {        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();        if (nums == null || nums.size() == 0) {            return result;        }        ArrayList<Integer> path = new ArrayList<Integer>();        dfs(result, path, nums);        return result;    }    private void dfs(ArrayList<ArrayList<Integer>> result, ArrayList<Integer> path,        ArrayList<Integer> nums) {        if (path.size() == nums.size()) {            result.add(new ArrayList<Integer>(path));            return;        }                            for (int i = 0; i < nums.size(); i++) {            if (path.contains(nums.get(i))) {                continue;            }            path.add(nums.get(i));            dfs(result, path, nums);            path.remove(path.size() - 1);        }    }

思路：

1. set大小一致

2. 无重复

3. 不需要pos信息

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