Code for How to permute a String

Dynamic Programming, Recursion, & Backtracking/permutations.java

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+/*
+
+
+  Permutation- LeetCode: https://leetcode.com/problems/sudoku-solver/
+
+  This code passes all Leetcode test cases as of Sep 2 2019 (12:18 pm)
+  Runtime: 1 ms*, faster than 97.78% of Java online submissions for Permutation.
+
+  The video(String version) to explain this code is here: https://www.youtube.com/watch?v=GCm7m5671Ps
+*/
+
+
+/*
+  Driver function to kick off the recursion
+*/
+public List<List<Integer>> permute(int[] nums) {
+
+   List<List<Integer>> result = new ArrayList<List<Integer>>();
+
+   ArrayList<Integer> decisionSpace = new ArrayList<Integer>();
+   for(int i : nums){
+      decisionSpace.add(i);
+    }
+
+   /* helper function to add all possible permuation to result list
+   */
+   permuteHelper(decisionSpace,new ArrayList<Integer>(), result) ;
+
+   return result;
+    }
+
+private void permuteHelper(ArrayList<Integer> decisionSpace, ArrayList<Integer> choosen, List<List<Integer>> result){
+
+        // Base case : If we have nothing to permute , we just add choosen list result
+        if(decisionSpace.size() == 0){
+            result.add(new ArrayList<Integer>(choosen));
+        }
+        else{
+            for(int i = 0; i < decisionSpace.size(); i++){
+                  // choose / explore / unchoose
+                    int valueSelected = decisionSpace.get(i);
+                    choosen.add(valueSelected);  // choosen
+                    decisionSpace.remove(i);
+                    permuteHelper(decisionSpace,choosen,result); // explored
+                    decisionSpace.add(i,valueSelected);
+                    choosen.remove(choosen.size()-1);  // unchoosen
+            }
+        }
+
+
+}