subsets add iterate, backtrack, binary sorted

Author: zgpeace

code/LeetCode/src/backtracking/Subsets.java

@@ -1,5 +1,6 @@
 package backtracking;
 
+import javax.annotation.Resource;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -10,7 +11,10 @@ public class Subsets {
   public static void main(String[] args) {
     int[] nums = new int[]{1,2,3};
     Subsets obj = new Subsets();
-    List<List<Integer>> resultList = obj.subsets(nums);
+    //List<List<Integer>> resultList = obj.subsets(nums);
+    //List<List<Integer>> resultList = obj.subsetsWithRecursion(nums);
+    //List<List<Integer>> resultList = obj.subsetsWithBacktrack(nums);
+    List<List<Integer>> resultList = obj.subsetsWithBinarySorted(nums);
     System.out.println(Arrays.toString(resultList.toArray()));
   }
 
@@ -37,4 +41,70 @@ private void dfs(int[] nums, List<List<Integer>> resultList, List<Integer> list,
     list.remove(list.size() - 1);
     dfs(nums, resultList, list, index + 1);
   }
+
+
+  public List<List<Integer>> subsetsWithRecursion(int[] nums) {
+    List<List<Integer>> outputList = new ArrayList<List<Integer>>();
+    outputList.add(new ArrayList<Integer>());
+    for (int num: nums) {
+      List<List<Integer>> newList = new ArrayList<List<Integer>>();
+      for (List<Integer> list: outputList) {
+        newList.add(new ArrayList<Integer>(list) {{ add(num); }});
+      }
+
+      for (List<Integer> list: newList) {
+        outputList.add(list);
+      }
+    }
+
+    return outputList;
+  }
+
+  public List<List<Integer>> subsetsWithBacktrack(int[] nums) {
+    List<List<Integer>> resultList = new ArrayList<List<Integer>>();
+    for (int len = 0; len <= nums.length; len++) {
+      // backtrack
+      backtrack(nums, resultList, new ArrayList<Integer>(), 0, len);
+    }
+
+    return resultList;
+  }
+
+  private void backtrack(int[] nums, List<List<Integer>> resultList, List<Integer> list, int first, int len) {
+    // exit
+    if (list.size() == len) {
+      resultList.add(new ArrayList<Integer>(list));
+      return;
+    }
+
+    if (first == nums.length) {
+      return;
+    }
+    list.add(nums[first]);
+    backtrack(nums, resultList, list, first + 1, len);
+    list.remove(list.size() - 1);
+    backtrack(nums, resultList, list, first + 1, len);
+  }
+
+  public List<List<Integer>> subsetsWithBinarySorted(int[] nums) {
+    List<List<Integer>> resultList = new ArrayList<List<Integer>>();
+    int n = nums.length;
+
+    for (int i = (int)Math.pow(2, n); i < (int)Math.pow(2, n + 1); i++) {
+      // generate bitmask, from 0..00 to 1..11
+      String bitmask = Integer.toBinaryString(i).substring(1);
+
+      // append subset corresponding to that bitmask
+      List<Integer> list = new ArrayList<Integer>();
+      for (int k = 0; k < n; k++) {
+        if (bitmask.charAt(k) == '1') {
+          list.add(nums[k]);
+        }
+      }
+
+      resultList.add(list);
+    }
+
+    return resultList;
+  }
 }