Merge pull request #593 from jdalma/main

[정현준] 14주차

Author: jdalma

binary-tree-level-order-traversal/jdalma.kt

@@ -0,0 +1,63 @@
+package leetcode_study
+
+import io.kotest.matchers.shouldBe
+import org.junit.jupiter.api.Test
+
+class `binary-tree-level-order-traversal` {
+
+    fun levelOrder(root: TreeNode?): List<List<Int>> {
+        return if (root == null) emptyList()
+        else usingDFS(root)
+    }
+
+    /**
+     * TC: O(n), SC: O(n)
+     */
+    private fun usingBFS(root: TreeNode): List<List<Int>> {
+        val queue = ArrayDeque<TreeNode>().apply {
+            this.add(root)
+        }
+
+        val result = mutableListOf<List<Int>>()
+        while (queue.isNotEmpty()) {
+            val values = mutableListOf<Int>()
+            repeat(queue.size) {
+                val node = queue.removeFirst()
+                values.add(node.`val`)
+                node.left?.also { queue.add(it) }
+                node.right?.also { queue.add(it) }
+            }
+            result.add(values)
+        }
+
+        return result
+    }
+
+    /**
+     * TC: O(n), SC: O(n)
+     */
+    private fun usingDFS(root: TreeNode): List<List<Int>> {
+
+        fun dfs(node: TreeNode, result: MutableList<MutableList<Int>>, depth: Int) {
+            if (depth >= result.size) {
+                result.add(mutableListOf())
+            }
+            result[depth].add(node.`val`)
+            node.left?.also { dfs(it, result, depth + 1) }
+            node.right?.also { dfs(it, result, depth + 1) }
+        }
+
+        return mutableListOf<MutableList<Int>>().apply {
+            dfs(root, this, 0)
+        }
+    }
+
+    @Test
+    fun `트리 노드를 깊이 별로 반환한다`() {
+        levelOrder(TreeNode.of(3,9,20,null,null,15,7)) shouldBe listOf(
+            listOf(3),
+            listOf(9,20),
+            listOf(15,7)
+        )
+    }
+}