Create 0173-binary-search-tree-iterator.swift

Author: drxlx

swift/0173-binary-search-tree-iterator.swift

@@ -0,0 +1,55 @@
+/**
+ * Question Link: https://leetcode.com/problems/binary-search-tree-iterator/
+ */
+
+ /**
+ * 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 BSTIterator {
+    var cur: TreeNode?
+    var stack: [TreeNode]
+
+    init(_ root: TreeNode?) {
+        self.cur = root
+        self.stack = []
+    }
+    
+    func next() -> Int {
+        while cur != nil || !stack.isEmpty {
+            if cur != nil {
+                stack.append(cur!)
+                cur = cur?.left
+            } else {
+                cur = stack.popLast()
+                let res = cur?.val ?? 0
+                cur = cur?.right
+                return res
+            }
+        }
+        return -1
+    }
+    
+    func hasNext() -> Bool {
+        cur != nil || !stack.isEmpty
+    }
+}
+
+/**
+ * Your BSTIterator object will be instantiated and called as such:
+ * let obj = BSTIterator(root)
+ * let ret_1: Int = obj.next()
+ * let ret_2: Bool = obj.hasNext()
+ */