feat(algorithms): add rotate_image

Author: WindomZ

README.md

@@ -24,6 +24,7 @@
 
 | # | Problem | Solution | Difficulty | Single Repetition Duration | LeetCode Run Time |
 | ---: | :----- | :--------: | :----------: | ----------: | ----------: |
+|48|[Rotate Image][Algorithms-48]|[WindomZ][Algorithms-48-Go]|Medium|[12.1 ns/op/3 test cases][Algorithms-48-Test]|3 ms|
 |47|[Permutations II][Algorithms-47]|[WindomZ][Algorithms-47-Go]|Medium|[531 ns/op/3 test cases][Algorithms-47-Test]|19 ms|
 |46|[Permutations][Algorithms-46]|[WindomZ][Algorithms-46-Go]|Medium|[1713 ns/op/3 test cases][Algorithms-46-Test]|9 ms|
 |45|[Jump Game II][Algorithms-45]|[WindomZ][Algorithms-45-Go]|Hard|[19.6 ns/op/6 test cases][Algorithms-45-Test]|19 ms|
@@ -100,6 +101,9 @@ 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.
 
+[Algorithms-48-Test]:algorithms/rotate_image/rotate_test.go#L43
+[Algorithms-48-Go]:algorithms/rotate_image/rotate.go
+[Algorithms-48]:https://leetcode.com/rotate-image/
 [Algorithms-47-Test]:algorithms/permutations_ii/permuteUnique_test.go#L53
 [Algorithms-47-Go]:algorithms/permutations_ii/permuteUnique.go
 [Algorithms-47]:https://leetcode.com/permutations-ii/

algorithms/rotate_image/rotate.go

@@ -0,0 +1,22 @@
+package rotateimage
+
+// rotate clockwise rotate
+// flip the matrix vertically, then flip it symmetrically
+// 1 2 3    7 8 9    7 4 1
+// 4 5 6 => 4 5 6 => 8 5 2
+// 7 8 9    1 2 3    9 6 3
+func rotate(matrix [][]int) {
+	// flip the matrix vertically
+	for i := 0; i < len(matrix)/2; i++ {
+		for j := 0; j < len(matrix); j++ {
+			matrix[i][j], matrix[len(matrix)-i-1][j] =
+				matrix[len(matrix)-i-1][j], matrix[i][j] // swap
+		}
+	}
+	// flip it symmetrically
+	for i := 0; i < len(matrix); i++ {
+		for j := i; j < len(matrix); j++ {
+			matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j] // swap
+		}
+	}
+}

algorithms/rotate_image/rotate_test.go

@@ -0,0 +1,63 @@
+package rotateimage
+
+import (
+	"testing"
+
+	"github.com/WindomZ/testify/assert"
+)
+
+func Test_rotate(t *testing.T) {
+	var matrix [][]int
+
+	matrix = [][]int{}
+	rotate(matrix)
+	assert.Equal(t, [][]int{}, matrix)
+
+	matrix = [][]int{
+		{1, 2, 3},
+		{4, 5, 6},
+		{7, 8, 9},
+	}
+	rotate(matrix)
+	assert.Equal(t, [][]int{
+		{7, 4, 1},
+		{8, 5, 2},
+		{9, 6, 3},
+	}, matrix)
+
+	matrix = [][]int{
+		{5, 1, 9, 11},
+		{2, 4, 8, 10},
+		{13, 3, 6, 7},
+		{15, 14, 12, 16},
+	}
+	rotate(matrix)
+	assert.Equal(t, [][]int{
+		{15, 13, 2, 5},
+		{14, 3, 4, 1},
+		{12, 6, 8, 9},
+		{16, 7, 10, 11},
+	}, matrix)
+}
+
+func Benchmark_rotate(b *testing.B) {
+	b.StopTimer()
+	b.ReportAllocs()
+	b.StartTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			rotate([][]int{})
+			rotate([][]int{
+				{1, 2, 3},
+				{4, 5, 6},
+				{7, 8, 9},
+			})
+			rotate([][]int{
+				{5, 1, 9, 11},
+				{2, 4, 8, 10},
+				{13, 3, 6, 7},
+				{15, 14, 12, 16},
+			})
+		}
+	})
+}