题目
给定一个没有重复数字的序列，返回其所有可能的全排列。
示例:
输入: [1,2,3]
输出:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]
class Solution {
public static List<List<Integer>> permute(int[] nums) {
List<List<Integer>> res = new ArrayList<>();
if (nums == null || nums.length == 0) return res;
helper2(res, 0, nums);
return res;
}
public static void helper2(List<List<Integer>> res, int start, int[] nums) {
if (start == nums.length) {
List<Integer> list = new ArrayList<>();
for (int num : nums) {
list.add(num);
}
res.add(new ArrayList<>(list));
return;
}
for (int i = start; i < nums.length; i++) {
swap(nums, start, i);
helper2(res, start + 1, nums);
swap(nums, start, i);
}
}
public static void swap(int[] nums, int l, int r) {
int temp = nums[l];
nums[l] = nums[r];
nums[r] = temp;
}
}
