0046-permutations.java

importjava.util.ArrayList;
importjava.util.Arrays;

classSolution {

publicList<List<Integer>> permute(int[] nums) {
List<List<Integer>> ans = newArrayList<>();
function(ans, nums, 0);
returnans;
 }

publicvoidfunction(List<List<Integer>> ans, int[] arr, intstart) {
if (start == arr.length) {
List<Integer> list = newArrayList();
for (inti = 0; i < arr.length; i++) list.add(arr[i]);
ans.add(list);
return;
 }

for (inti = start; i < arr.length; i++) {
swap(arr, start, i);
function(ans, arr, start + 1);
swap(arr, start, i);
 }
 }

publicvoidswap(int[] arr, inta, intb) {
inttemp = arr[a];
arr[a] = arr[b];
arr[b] = temp;
 }
}