feat: add swift implementation to lcof problem: No.07 (#2854)

Author: klever34

lcof/面试题07. 重建二叉树/README.md

@@ -350,6 +350,50 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+/* public class TreeNode {
+*     public var val: Int
+*     public var left: TreeNode?
+*     public var right: TreeNode?
+*     public init(_ val: Int) {
+*         self.val = val
+*         self.left = nil
+*         self.right = nil
+*     }
+*  }
+*/
+
+class Solution {
+    private var d = [Int: Int]()
+    private var preorder: [Int] = []
+    private var inorder: [Int] = []
+
+    func buildTree(_ preorder: [Int], _ inorder: [Int]) -> TreeNode? {
+        let n = inorder.count
+        for i in 0..<n {
+            d[inorder[i]] = i
+        }
+        self.preorder = preorder
+        self.inorder = inorder
+        return dfs(0, 0, n)
+    }
+
+    private func dfs(_ i: Int, _ j: Int, _ n: Int) -> TreeNode? {
+        if n < 1 {
+            return nil
+        }
+        let k = d[preorder[i]]!
+        let l = k - j
+        let root = TreeNode(preorder[i])
+        root.left = dfs(i + 1, j, l)
+        root.right = dfs(i + 1 + l, k + 1, n - l - 1)
+        return root
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题07. 重建二叉树/Solution.swift

@@ -0,0 +1,39 @@
+/* public class TreeNode {
+*     public var val: Int
+*     public var left: TreeNode?
+*     public var right: TreeNode?
+*     public init(_ val: Int) {
+*         self.val = val
+*         self.left = nil
+*         self.right = nil
+*     }
+*  }
+*/
+
+class Solution {
+    private var d = [Int: Int]()
+    private var preorder: [Int] = []
+    private var inorder: [Int] = []
+
+    func buildTree(_ preorder: [Int], _ inorder: [Int]) -> TreeNode? {
+        let n = inorder.count
+        for i in 0..<n {
+            d[inorder[i]] = i
+        }
+        self.preorder = preorder
+        self.inorder = inorder
+        return dfs(0, 0, n)
+    }
+
+    private func dfs(_ i: Int, _ j: Int, _ n: Int) -> TreeNode? {
+        if n < 1 {
+            return nil
+        }
+        let k = d[preorder[i]]!
+        let l = k - j
+        let root = TreeNode(preorder[i])
+        root.left = dfs(i + 1, j, l)
+        root.right = dfs(i + 1 + l, k + 1, n - l - 1)
+        return root
+    }
+}