添加 257. 二叉树的所有路径 Swift版本

Author: qxuewei

problems/0257.二叉树的所有路径.md

@@ -581,7 +581,72 @@ var binaryTreePaths = function(root) {
 };  
 ```
 
+Swift:
+
+> 递归/回溯
+```swift
+func binaryTreePaths(_ root: TreeNode?) -> [String] {
+    var res = [String]()
+    guard let root = root else {
+        return res
+    }
+    var path = [Int]()
+    _binaryTreePaths(root, path: &path, res: &res)
+    return res
+}
+func _binaryTreePaths(_ root: TreeNode, path: inout [Int], res: inout [String]) {
+    path.append(root.val)
+    if root.left ==  nil && root.right == nil {
+        var str = ""
+        for i in 0 ..< path.count - 1 {
+            str.append("\(path[i])->")
+        }
+        str.append("\(path.last!)")
+        res.append(str)
+        return
+    }
+    if let left = root.left {
+        _binaryTreePaths(left, path: &path, res: &res)
+        path.removeLast()
+    }
+    if let right = root.right {
+        _binaryTreePaths(right, path: &path, res: &res)
+        path.removeLast()
+    }
+}
+```
 
+> 迭代
+```swift
+func binaryTreePaths(_ root: TreeNode?) -> [String] {
+    var res = [String]()
+    guard let root = root else {
+        return res
+    }
+    var stackNode = [TreeNode]()
+    stackNode.append(root)
+    
+    var stackStr = [String]()
+    stackStr.append("\(root.val)")
+    
+    while !stackNode.isEmpty {
+        let node = stackNode.popLast()!
+        let str = stackStr.popLast()!
+        if node.left == nil && node.right == nil {
+            res.append(str)
+        }
+        if let left = node.left {
+            stackNode.append(left)
+            stackStr.append("\(str)->\(left.val)")
+        }
+        if let right = node.right {
+            stackNode.append(right)
+            stackStr.append("\(str)->\(right.val)")
+        }
+    }
+    return res
+}
+```
 
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