[Swift]LeetCode1028. 从先序遍历还原二叉树 | Recover a Tree From Preorder Traversal

 1 /**
 2  * DeFinition for a binary tree node.
 3  * public class TreeNode {
 4  *     public var val: Int
 5  *     public var left: TreeNode?
 6  *     public var right: TreeNode?
 7  *     public init(_ val: int) {
 8  *         self.val = val
 9  *         self.left = nil
10  *         self.right = nil
11  *     }
12  * }
13  */
14 class Solution {
15     var len:Int = 0
16     var s:[Character] = [Character]()
17     var pos:Int = 0
18     func recoverFromPreorder(_ S: String) -> TreeNode? {
19         len = s.count
20         s = Array(S)
21         return go(0)
22     }
23     
24     func go(_ dep:int) -> TreeNode?
25     {
26         var v:Int = 0
27         while(pos < len && s[pos] >= "0" && s[pos] <= "9")
28         {
29             v = v * 10 + (s[pos].ascii - 48)
30             pos += 1
31         }
32         var cur:TreeNode? = TreeNode(v)
33         if hasEdge(dep + 1)
34         {
35             pos += (dep + 1)
36             cur?.left = go(dep + 1)
37         }
38         if hasEdge(dep + 1)
39         {
40             pos += (dep + 1)
41             cur?.right = go(dep + 1)
42         }
43         return cur
44     }
45     
46     func hasEdge(_ d:int) -> Bool
47     {
48         if pos+d > len-1
49         {
50             return false            
51         }
52         for i in pos..<(pos + d)
53         {
54             if s[i] != "-"
55             {
56                 return false
57             }
58         }
59         return s[pos+d] != "-"
60     }
61 }
62 
63 //Character扩展 
64 extension Character  
65 {  
66   //Character转ASCII整数值(定义小写为整数值)
67    var ascii: Int {
68        get {
69            return Int(self.unicodeScalars.first?.value ?? 0)
70        }       
71     }
72 }