48: Rotate Image

Author: emanuelschmoczer

README.md

@@ -11,6 +11,7 @@ My solutions to LeetCode problems in Kotlin.
 |                    [8](https://leetcode.com/problems/string-to-integer-atoi/)                    |                 [String to Integer (atoi)](src/main/kotlin/com/schmoczer/leetcode/_0008/StringToInteger.kt)                  |   Medium   |
 |                      [20](https://leetcode.com/problems/valid-parentheses/)                      |                    [Valid Parentheses](src/main/kotlin/com/schmoczer/leetcode/_0020/ValidParentheses.kt)                     |    Easy    |
 |                     [42](https://leetcode.com/problems/trapping-rain-water/)                     |                   [Trapping Rain Water](src/main/kotlin/com/schmoczer/leetcode/_0042/TrappingRainWater.kt)                   |    Hard    |
+|                        [48](https://leetcode.com/problems/rotate-image/)                         |                         [Rotate Image](src/main/kotlin/com/schmoczer/leetcode/_0048/RotateImage.kt)                          |   Medium   |
 |                       [49](https://leetcode.com/problems/group-anagrams/)                        |                       [Group Anagrams](src/main/kotlin/com/schmoczer/leetcode/_0049/GroupAnagrams.kt)                        |   Medium   |
 |                      [73](https://leetcode.com/problems/set-matrix-zeroes/)                      |                     [Set Matrix Zeroes](src/main/kotlin/com/schmoczer/leetcode/_0073/SetMatrixZeroes.kt)                     |   Medium   |
 |                      [125](https://leetcode.com/problems/valid-palindrome/)                      |                     [Valid Palindrome](src/main/kotlin/com/schmoczer/leetcode/_0125/ValidPalindrome.kt)                      |    Easy    |

src/main/kotlin/com/schmoczer/leetcode/_0048/README.md

@@ -0,0 +1,24 @@
+# Rotate Image
+
+You are given an `n x n` 2D `matrix` representing an image, rotate the image by 90 degrees (clockwise).
+
+You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate
+another 2D matrix and do the rotation.
+
+Example 1:
+
+> Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
+>
+> Output: [[7,4,1],[8,5,2],[9,6,3]]
+
+Example 2:
+
+> Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
+>
+> Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
+
+Constraints:
+
+- `n == matrix.length == matrix[i].length`
+- `1 <= n <= 20`
+- `-1000 <= matrix[i][j] <= 1000`

src/main/kotlin/com/schmoczer/leetcode/_0048/RotateImage.kt

@@ -0,0 +1,44 @@
+package com.schmoczer.leetcode._0048
+
+class RotateImage {
+    // Runtime 0ms Beats 100.00%
+    fun rotate(matrix: Array<IntArray>) {
+        var i = 0
+        while (i < matrix.size - 1 - i) {
+            val width = matrix.size - i - 1
+            for (j in i until width) {
+                val up = matrix[i][j]
+                val right = matrix[j][width]
+                val down = matrix[width][matrix.size - 1 - j]
+                val left = matrix[matrix.size - 1 - j][i]
+                matrix[j][width] = up
+                matrix[width][matrix.size - 1 - j] = right
+                matrix[matrix.size - 1 - j][i] = down
+                matrix[i][j] = left
+            }
+            i++
+        }
+    }
+}
+
+// width = 4 - 0 = 4
+// i = 0, j = 0, right should be: (0, 3)
+// first: j = 0, second: width - 1 = 3?
+// down should be: (3, 3)
+// row: width - 1 = 3, column: width - 1 - j = 3
+// left should be: (3, 0)
+//
+// i = 0, j = 1, right should be: (1, 3)
+// first: j = 1, second: widht - 1 = 3
+// down should be (3, 2)
+// row: width - 1, column: width - 1 - j = 2
+// left should be (2, 0)
+//
+// i = 0, j = 2, right should (2, 3)
+//
+// width = 4 - 1 = 3
+// i = 1, j = 1, right should be (1, 2)
+// row: j = 1, column: width - 1 = 2
+// down should be (2, 2)
+// row: width - 1 = 2, column: width - 1 - j =
+// left should be (2, 1)

src/test/kotlin/com/schmoczer/leetcode/_0048/RotateImageTest.kt

@@ -0,0 +1,38 @@
+package com.schmoczer.leetcode._0048
+
+import org.junit.jupiter.api.BeforeEach
+import kotlin.test.Test
+import kotlin.test.assertContentEquals
+
+class RotateImageTest {
+    private lateinit var sut: RotateImage
+
+    @BeforeEach
+    fun setUp() {
+        sut = RotateImage()
+    }
+
+    @Test
+    fun `rotate 3x3 matrix`() {
+        val input = arrayOf(intArrayOf(1, 2, 3), intArrayOf(4, 5, 6), intArrayOf(7, 8, 9))
+        val expected = arrayOf(intArrayOf(7, 4, 1), intArrayOf(8, 5, 2), intArrayOf(9, 6, 3))
+
+        sut.rotate(input)
+
+        for (i in 0 until expected.size) {
+            assertContentEquals(expected[i], input[i])
+        }
+    }
+
+    @Test
+    fun `rotate 4x4 matrix`() {
+        val input = arrayOf(intArrayOf(5, 1, 9, 11), intArrayOf(2, 4, 8, 10), intArrayOf(13, 3, 6, 7), intArrayOf(15, 14, 12, 16))
+        val expected = arrayOf(intArrayOf(15, 13, 2, 5), intArrayOf(14, 3, 4, 1), intArrayOf(12, 6, 8, 9), intArrayOf(16, 7, 10, 11))
+
+        sut.rotate(input)
+
+        for (i in 0 until expected.size) {
+            assertContentEquals(expected[i], input[i])
+        }
+    }
+}