Permutations @ LeetCode

Package Level3; import java. util. arrayList;/*** Permutations ** Given a collection of numbers, return all possible permutations. for example, [, 3] have the following permutations: [, 3], [, 2], [, 3], [, 1], [, 1, 2], and [3, 2, 1]. **/public class S46 {public static void main (String [] args) {int [] S = {1, 2, 3}; System. out. println (permute (S);} public static ArrayList <Integ Er> permute (int [] S) {ArrayList <Integer> ret = new ArrayList <Integer> (); arrayList <Integer> list = new ArrayList <Integer> (); rec (S, ret, list); return ret;} public static void rec (int [] S, arrayList <Integer> ret, ArrayList <Integer> list) {// when the array length is 0, add the ret if (S. length = 0) {ret. add (new ArrayList <Integer> (list); // You must create an ArrayList Based on the field and add it to ret! Return;} // traverse each number in the array as the first element for (int I = 0; I <S. length; I ++) {// construct a new sub-array to recursion int [] sub = new int [S. length-1]; System. arraycopy (S, 0, sub, 0, I); System. arraycopy (S, I + 1, sub, I, S. length-i-1); // System. out. println (Arrays. toString (sub); list. add (S [I]); rec (sub, ret, list); list. remove (list. size ()-1); // restore site }}}