solve problem Subsets

Author: P-ppc

README.md

@@ -227,6 +227,7 @@ All solutions will be accepted!
 |46|[Permutations](https://leetcode-cn.com/problems/permutations/description/)|[java/py/js](./algorithms/Permutations)|Medium|
 |47|[Permutations II](https://leetcode-cn.com/problems/permutations-ii/description/)|[java/py/js](./algorithms/PermutationsII)|Medium|
 |77|[Combinations](https://leetcode-cn.com/problems/combinations/description/)|[java/py/js](./algorithms/Combinations)|Medium|
+|78|[Subsets](https://leetcode-cn.com/problems/subsets/description/)|[java/py/js](./algorithms/Subsets)|Medium|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/Subsets/README.md

@@ -0,0 +1,2 @@
+# Subsets
+This problem is easy to solve by Backtracking Algorithm

algorithms/Subsets/Solution.java

@@ -0,0 +1,18 @@
+class Solution {
+    public List<List<Integer>> subsets(int[] nums) {
+        List<List<Integer>> res = new ArrayList<List<Integer>>();
+        backTrack(0, nums, new ArrayList<Integer>(), res);
+        return res;
+    }
+    
+    public void backTrack(int beg, int[] nums, List<Integer> temp, List<List<Integer>> res) {
+        if (beg <= nums.length) {
+            res.add(temp);
+            for (int i = beg; i < nums.length; i++) {
+                List<Integer> t = new ArrayList<Integer>(temp);
+                t.add(nums[i]);
+                backTrack(i + 1, nums, t, res);
+            }
+        }
+    }
+}

algorithms/Subsets/solution.js

@@ -0,0 +1,20 @@
+/**
+ * @param {number[]} nums
+ * @return {number[][]}
+ */
+var subsets = function(nums) {
+    let res = []
+    backTrack(0, nums, [], res)
+    return res
+};
+
+var backTrack = function(beg, nums, temp, res) {
+    if (beg <= nums.length) {
+        res.push(temp)
+        for (let i = beg; i < nums.length; i++) {
+            let t = temp.slice()
+            t.push(nums[i])
+            backTrack(i + 1, nums, t, res)
+        }
+    }
+}

algorithms/Subsets/solution.py

@@ -0,0 +1,18 @@
+class Solution(object):
+    def subsets(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: List[List[int]]
+        """
+        res = []
+        self.backtrack(0, nums, [], res)
+        return res
+    
+    def backtrack(self, beg, nums, temp, res):
+        if beg <= len(nums):
+            res.append(temp)
+            for i in xrange(beg, len(nums)):
+                num = nums[i]
+                t = temp[:]
+                t.append(num)
+                self.backtrack(i + 1, nums, t, res)