[SeongA] WEEK 04 solutions

maximum-depth-of-binary-tree/delight010.swift

@@ -0,0 +1,26 @@
+class Solution {
+    func maxDepth(_ root: TreeNode?) -> Int {
+        if root == nil {
+            return 0
+        }
+
+        var level = 0
+        var stack: [(TreeNode?, Int)] = [(root, 1)]
+
+        while !stack.isEmpty {
+            let (current, count) = stack.removeLast()
+            if current?.left == nil && current?.right == nil {
+                level = max(level, count)
+            }
+            if let right = current?.right {
+                stack.append((right, count + 1))
+            }
+            if let left = current?.left {
+                stack.append((left, count + 1))
+            }
+        }
+
+        return level
+    }
+}
+

merge-two-sorted-lists/delight010.swift

@@ -0,0 +1,26 @@
+public class ListNode {
+    public var val: Int
+    public var next: ListNode?
+    public init() { self.val = 0; self.next = nil; }
+    public init(_ val: Int) { self.val = val; self.next = nil; }
+    public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
+}
+
+class Solution {
+    func mergeTwoLists(_ list1: ListNode?, _ list2: ListNode?) -> ListNode? {
+        guard let list1 = list1 else {
+            return list2
+        }
+        guard let list2 = list2 else {
+            return list1
+        }
+
+        if list1.val < list2.val {
+            list1.next = mergeTwoLists(list1.next, list2)
+        } else {
+            list2.next = mergeTwoLists(list2.next, list1)
+        }
+        return list1.val < list2.val ? list1 : list2
+    }
+}
+