Adding 572. Subtree of Another Tree in Swift

Author: Mahim1997

swift/572-Subtree-of-Another-Tree.swift

@@ -0,0 +1,48 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init() { self.val = 0; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+ *         self.val = val
+ *         self.left = left
+ *         self.right = right
+ *     }
+ * }
+ */
+class Solution {
+    private func areSameTrees(
+        _ node1: TreeNode?, 
+        _ node2: TreeNode?
+    ) -> Bool {
+        // if both are nil, they are same
+        if node1 == nil && node2 == nil { return true }
+        
+        // if anyone else is nil, they are not the same
+        guard let node1 = node1 else { return false }
+        guard let node2 = node2 else { return false }
+        
+        return (
+            (node1.val == node2.val) &&
+            areSameTrees(node1.left, node2.left) &&
+            areSameTrees(node1.right, node2.right)
+        )
+    }
+    
+    func isSubtree(_ root: TreeNode?, _ subRoot: TreeNode?) -> Bool {
+        // Base cases (both can be nil, just any one can't)
+        if root == nil && subRoot == nil { return true }
+        guard let root = root else { return false }
+        guard let subRoot = subRoot else { return false }
+        
+        // Base case: Exactly same tree
+        if areSameTrees(root, subRoot) { return true }
+        
+        // Recursive
+        return isSubtree(root.left, subRoot) 
+                || isSubtree(root.right, subRoot)
+    }
+}