feat(solutions): add subsets

Author: WindomZ

README.md

@@ -25,6 +25,7 @@
 
 | # | Problem | Solution | Difficulty | Single Repetition Duration | LeetCode Run Time |
 | ---: | :----- | :--------: | :----------: | ----------: | ----------: |
+|78|[Subsets][Solutions-78]|[WindomZ][Solutions-78-golang]|Medium|[447 ns/op/5 test cases][Solutions-78-Test]|6 ms|
 |77|[Combinations][Solutions-77]|[WindomZ][Solutions-77-golang]|Medium|[336 ns/op/6 test cases][Solutions-77-Test]|246 ms|
 |75|[Sort Colors][Solutions-75]|[WindomZ][Solutions-75-golang]|Medium|[13.4 ns/op/6 test cases][Solutions-75-Test]|3 ms|
 |74|[Search a 2D Matrix][Solutions-74]|[WindomZ][Solutions-74-golang]|Medium|[32.5 ns/op/6 test cases][Solutions-74-Test]|16 ms|
@@ -129,6 +130,9 @@ Welcome to report bugs, suggest ideas and discuss on [issues page](https://githu
 ### Support
 If you like it then you can put a :star:Star on it.
 
+[Solutions-78]:https://leetcode.com/problems/subsets/
+[Solutions-78-golang]:solutions/subsets/subsets.go
+[Solutions-78-Test]:solutions/subsets/subsets_test.go#L62
 [Solutions-77]:https://leetcode.com/problems/combinations/
 [Solutions-77-golang]:solutions/combinations/combinations.go
 [Solutions-77-Test]:solutions/combinations/combinations_test.go#L32

solutions/subsets/README.md

@@ -0,0 +1,27 @@
+# 78. Subsets
+
+[Description](https://leetcode.com/problems/subsets/description/) | 
+[Discuss](https://leetcode.com/problems/subsets/discuss/) | 
+[Solution](https://leetcode.com/problems/subsets/solution/)
+
+## Description
+
+Given a set of **distinct** integers, _nums_, return all possible subsets (the power set).
+
+**Note:** The solution set must not contain duplicate subsets.
+
+For example,  
+
+If **_nums_** = `[1,2,3]`, a solution is:
+```
+[
+  [3],
+  [1],
+  [2],
+  [1,2,3],
+  [1,3],
+  [2,3],
+  [1,2],
+  []
+]
+```

solutions/subsets/subsets.go

@@ -0,0 +1,33 @@
+package subsets
+
+// like: {1, 2, 3}
+// 0) 0 0 0  -> {}
+// 1) 0 0 1  -> {1}
+// 2) 0 1 0  -> {2}
+// 3) 0 1 1  -> {1,2}
+// 4) 1 0 0  -> {3}
+// 5) 1 0 1  -> {1,3}
+// 6) 1 1 0  -> {2,3}
+// 7) 1 1 1  -> {1,2,3}
+
+func subsets(nums []int) [][]int {
+	if len(nums) == 0 {
+		return [][]int{}
+	}
+
+	count := 2
+	for i := 1; i < len(nums); i++ {
+		count *= 2 // count of result is 2^N
+	}
+	result := make([][]int, count)
+	result[0] = []int{}
+
+	for i := 0; i < len(nums); i++ {
+		for j := 1; j < count; j++ {
+			if (uint(j)>>uint(i))&1 != 0 { // 2^N possible outcomes
+				result[j] = append(result[j], nums[i])
+			}
+		}
+	}
+	return result
+}

solutions/subsets/subsets_test.go

@@ -0,0 +1,75 @@
+package subsets
+
+import (
+	"testing"
+
+	"github.com/WindomZ/testify/assert"
+)
+
+func Test_subsets(t *testing.T) {
+	assert.Equal(t,
+		[][]int{}, subsets([]int{}))
+
+	assert.Equal(t,
+		[][]int{
+			{},
+			{1},
+			{2},
+			{1, 2},
+		}, subsets([]int{1, 2}))
+
+	assert.Equal(t,
+		[][]int{
+			{},
+			{2},
+			{3},
+			{2, 3},
+		}, subsets([]int{2, 3}))
+
+	assert.Equal(t,
+		[][]int{
+			{},
+			{1},
+			{2},
+			{1, 2},
+			{3},
+			{1, 3},
+			{2, 3},
+			{1, 2, 3},
+		}, subsets([]int{1, 2, 3}))
+
+	assert.Equal(t,
+		[][]int{
+			{},
+			{1},
+			{2},
+			{1, 2},
+			{3},
+			{1, 3},
+			{2, 3},
+			{1, 2, 3},
+			{5},
+			{1, 5},
+			{2, 5},
+			{1, 2, 5},
+			{3, 5},
+			{1, 3, 5},
+			{2, 3, 5},
+			{1, 2, 3, 5},
+		}, subsets([]int{1, 2, 3, 5}))
+}
+
+func Benchmark_subsets(b *testing.B) {
+	b.StopTimer()
+	b.ReportAllocs()
+	b.StartTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			subsets([]int{})
+			subsets([]int{1})
+			subsets([]int{2, 3})
+			subsets([]int{1, 2, 3})
+			subsets([]int{1, 2, 3, 5})
+		}
+	})
+}