Permutaitons

Solution.java

class Solution {
  
  public List<List<Integer>> permute(int[] nums) {
    List<List<Integer>> result = new ArrayList<>();
    permute(0, nums, result);
    return result;
  }
  
  private void permute(int depth, int[] nums, List<List<Integer>> result) {
    // base case
    if (depth == nums.length) {
      List<Integer> list = new ArrayList<>();
      for (int val : nums) list.add(val);
      result.add(list);
      return;
    }
    // enumeration
    for (int i = depth; i < nums.length; ++i) {
      swap(nums, depth, i);
      permute(depth + 1, nums, result);
      swap(nums, depth, i);
    }
  }
  
  private void swap(int[] nums, int i, int j) {
    int temp = nums[i];
    nums[i] = nums[j];
    nums[j] = temp;
  }
  
  
}