finish "78. Subsets". Fix #78

Author: diguage

README.adoc

@@ -393,12 +393,12 @@
 //|{leetcode_base_url}/combinations/[Combinations]
 //|{source_base_url}/Combinations.java[Java]
 //|Medium
-//
-//|78
-//|{leetcode_base_url}/subsets/[Subsets]
-//|{source_base_url}/Subsets.java[Java]
-//|Medium
-//
+
+|78
+|{leetcode_base_url}/subsets/[Subsets]
+|{source_base_url}/Subsets.java[Java]
+|Medium
+
 //|79
 //|{leetcode_base_url}/word-search/[Word Search]
 //|{source_base_url}/WordSearch.java[Java]

src/main/java/com/diguage/algorithm/leetcode/Subsets.java

@@ -0,0 +1,89 @@
+package com.diguage.algorithm.leetcode;
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+/**
+ * = 78. Subsets
+ *
+ * https://leetcode.com/problems/subsets/[Subsets - LeetCode]
+ *
+ * Given a set of *distinct* integers, nums, return all possible subsets (the power set).
+ *
+ * *Note:* The solution set must not contain duplicate subsets.
+ *
+ * .Example:
+ * [source]
+ * ----
+ * Input: nums = [1,2,3]
+ * Output:
+ * [
+ *   [3],
+ *   [1],
+ *   [2],
+ *   [1,2,3],
+ *   [1,3],
+ *   [2,3],
+ *   [1,2],
+ *   []
+ * ]
+ * ----
+ *
+ * @author D瓜哥, https://www.diguage.com/
+ * @since 2020-01-02 19:56
+ */
+public class Subsets {
+    /**
+     * Runtime: 0 ms, faster than 100.00% of Java online submissions for Subsets.
+     * 
+     * Memory Usage: 37.1 MB, less than 99.18% of Java online submissions for Subsets.
+     */
+    public List<List<Integer>> subsets(int[] nums) {
+        List<List<Integer>> result = new ArrayList<>();
+        result.add(new ArrayList<>());
+        for (int num : nums) {
+            List<List<Integer>> newSubsets = new ArrayList<>();
+            for (List<Integer> current : result) {
+                ArrayList<Integer> integers = new ArrayList<>(current);
+                integers.add(num);
+                newSubsets.add(integers);
+            }
+            result.addAll(newSubsets);
+        }
+        return result;
+    }
+
+    /**
+     * Runtime: 74 ms, faster than 5.06% of Java online submissions for Subsets.
+     *
+     * Memory Usage: 50.3 MB, less than 5.74% of Java online submissions for Subsets.
+     */
+    public List<List<Integer>> subsetsLevel(int[] nums) {
+        if (Objects.isNull(nums) || nums.length == 0) {
+            return Collections.emptyList();
+        }
+        Set<Set<Integer>> subsets = new HashSet<>();
+        subsets.add(Collections.emptySet());
+        for (int i = 0; i < nums.length; i++) {
+            ArrayList<Set<Integer>> list = new ArrayList<>(subsets);
+            list.forEach(s -> {
+                for (int num : nums) {
+                    Set<Integer> set = new TreeSet<>(s);
+                    set.add(num);
+                    subsets.add(set);
+                }
+            });
+        }
+        List<List<Integer>> result = subsets.stream()
+                .map(ArrayList::new)
+                .collect(Collectors.toList());
+        return result;
+    }
+
+    public static void main(String[] args) {
+        Subsets solution = new Subsets();
+        int[] a1 = {1, 2, 3};
+        List<List<Integer>> r1 = solution.subsets(a1);
+        System.out.println(r1);
+    }
+}