Add 54. Spiral Matrix solution

Author: enginebai

leetcode/146.lru-cache.md

@@ -5,19 +5,19 @@
 2. We will put the sentinel node at head and tail (always be there and we don't move the two ponters) to prevent extra null/empty check.
 
 ```js
-sentinel -> sentinel
+sentinel <-> sentinel
 [head]      [tail]
 
 // Insert 1 at first
-sentinel -> 1 -> sentinel
+sentinel <-> 1 <-> sentinel
 [head]           [tail]
 
 // Insert 2 at last
-sentinel -> 1 -> 2 -> sentinel
+sentinel <-> 1 <-> 2 <-> sentinel
 [head]                [tail]
 
 // Remove 2, 1 at last
-sentinel -> sentinel
+sentinel <-> sentinel
 [head]      [tail]
 ```
 

leetcode/54.spiral-matrix.md

@@ -0,0 +1,36 @@
+## [54. Spiral Matrix](https://leetcode.com/problems/spiral-matrix/)
+
+```kotlin
+fun spiralOrder(matrix: Array<IntArray>): List<Int> {
+    val elements = mutableListOf<Int>()
+    val m = matrix.size
+    val n = matrix[0].size
+    val directions = arrayOf(
+        intArrayOf(0, 1),   // Right
+        intArrayOf(1, 0),   // Down
+        intArrayOf(0, -1),  // Left
+        intArrayOf(-1, 0)   // UP
+    )
+    
+    val visited = Array(m) { _ -> BooleanArray(n) }
+    var direction = 0
+    var row = 0
+    var col = 0
+    while (elements.size < m * n) {
+        elements.add(matrix[row][col])
+        visited[row][col] = true
+        
+        val newRow = row + directions[direction][0]
+        val newCol = col + directions[direction][1]
+        
+        if (newRow < 0 || newRow >= m || newCol < 0 || newCol >= n || visited[newRow][newCol]) {
+            direction = (direction + 1) % directions.size
+        }
+        
+        row += directions[direction][0]
+        col += directions[direction][1]
+    }
+    
+    return elements
+}
+```

topics/problems-solutions.md

@@ -10,6 +10,7 @@
 |[217. Contains Duplicate](../leetcode/217.contains-duplicate.md)|Easy|
 |[350. Intersection of Two Arrays II](../leetcode/350.intersection-of-two-arrays-ii.md)|Easy|
 |[48. Rotate Image](../leetcode/48.rotate-image.md)|Medium|
+|[54. Spiral Matrix](../leetcode/54.spiral-matrix.md)|Medium|
 |[59. Spiral Matrix II](../leetcode/59.spiral-matrix-ii.md)|Medium|
 |[189. Rotate Array](../leetcode/189.rotate-array.md)|Medium|
 |[136. Single Number](../leetcode/136.single-number.md)|Easy|
@@ -26,7 +27,6 @@
 |[76. Minimum Window Substring](../leetcode/76.minimum-window-substring.md)|Hard|
 |[239. Sliding Window Maximum](../leetcode/239.sliding-window-maximium.md)|Hard|
 
-> * https://leetcode.com/problems/spiral-matrix/ 7k m
 > * https://leetcode.com/problems/find-all-duplicates-in-an-array/ 6k m
 > * https://leetcode.com/problems/merge-intervals/ 14k m
 > * https://leetcode.com/problems/container-with-most-water/ 17k m