Merge pull request youngyangyang04#1078 from qxuewei/master

添加 二叉树：以为使用了递归，其实还隐藏着回溯 Swift版本

Author: youngyangyang04

problems/二叉树中递归带着回溯.md

@@ -515,6 +515,61 @@ var binaryTreePaths = function(root) {
 };
 ```
 
+Swift：
+> 100.相同的树
+```swift
+// 递归
+func isSameTree(_ p: TreeNode?, _ q: TreeNode?) -> Bool {
+    return _isSameTree3(p, q)
+}
+func _isSameTree3(_ p: TreeNode?, _ q: TreeNode?) -> Bool {
+    if p == nil && q == nil {
+        return true
+    } else if p == nil && q != nil {
+        return false
+    } else if p != nil && q == nil {
+        return false
+    } else if p!.val != q!.val {
+        return false
+    }
+    let leftSide = _isSameTree3(p!.left, q!.left)
+    let rightSide = _isSameTree3(p!.right, q!.right)
+    return leftSide && rightSide
+}
+```
+
+> 257.二叉树的不同路径
+```swift
+// 递归/回溯
+func binaryTreePaths(_ root: TreeNode?) -> [String] {
+    var res = [String]()
+    guard let root = root else {
+        return res
+    }
+    var paths = [Int]()
+    _binaryTreePaths3(root, res: &res, paths: &paths)
+    return res
+}
+func _binaryTreePaths3(_ root: TreeNode, res: inout [String], paths: inout [Int]) {
+    paths.append(root.val)
+    if root.left == nil && root.right == nil {
+        var str = ""
+        for i in 0 ..< (paths.count - 1) {
+            str.append("\(paths[i])->")
+        }
+        str.append("\(paths.last!)")
+        res.append(str)
+    }
+    if let left = root.left {
+        _binaryTreePaths3(left, res: &res, paths: &paths)
+        paths.removeLast()
+    }
+    if let right = root.right {
+        _binaryTreePaths3(right, res: &res, paths: &paths)
+        paths.removeLast()
+    }
+}
+```
 
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