Permutations (no entry duplicate ) - https://leetcode.com/problems/permutations/description/

gistfile1.txt

class Solution {
    public List<List<Integer>> permute(int[] nums) {
      List<List<Integer>> results = new ArrayList<List<Integer>>();
      
      if (nums == null || nums.length == 0) {
        return results;
      }
      
      List<Integer> prefix = new ArrayList<Integer>();
      permutateRecursive(nums, prefix, results);
      
      return results;
    }
  
    private void permutateRecursive(int[] nums, List<Integer> prefix, List<List<Integer>> results) {
      
      // Stopping condition
      if (prefix.size() == nums.length) {
        results.add(new ArrayList<Integer>(prefix));
        return;
      }
      
      // Start moving elements
      for (int i = 0; i < nums.length; i++) {
        if (prefix.contains(nums[i]))
          continue;
        
        prefix.add(nums[i]);
        permutateRecursive(nums, prefix, results);
        
        // Dont forget to remove within same level of prefix.
        prefix.remove(prefix.size() - 1);
      }
    }
}