LeetCodeブラシ問題メモPermutaions

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public class Solution {
    public ArrayList<ArrayList<Integer>> permute(int[] num) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();

        //start from an empty list
        result.add(new ArrayList<Integer>());

        for (int i = 0; i < num.length; i++) {
            //list of list in current iteration of the array num
            ArrayList<ArrayList<Integer>> current = new ArrayList<ArrayList<Integer>>();
for (ArrayList<Integer> l : result) {
                // # of locations to insert is largest index + 1
                for (int j = 0; j < l.size()+1; j++) {
                    // + add num[i] to different locations
                    l.add(j, num[i]);

                    ArrayList<Integer> temp = new ArrayList<Integer>(l);
                    current.add(temp);

                    // - remove num[i] add
                    l.remove(j);
                }
            }

            result = new ArrayList<ArrayList<Integer>>(current);
        }

        return result;
    }
}