[Swift]LeetCode617. 合併二叉樹 | Merge Two Binary Trees

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Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not.

You need to merge them into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged node. Otherwise, the NOT null node will be used as the node of new tree.

Example 1:

Input: 
	Tree 1                     Tree 2                  
          1                         2                             
         / \                       / \                            
        3   2                     1   3                        
       /                           \   \                      
      5                             4   7                  
Output: 
Merged tree:
	     3
	    / \
	   4   5
	  / \   \ 
	 5   4   7

Note: The merging process must start from the root nodes of both trees.

---

給定兩個二叉樹，想象當你將它們中的一個覆蓋到另外一個上時，兩個二叉樹的一些節點便會重疊。

你須要將他們合併爲一個新的二叉樹。合併的規則是若是兩個節點重疊，那麼將他們的值相加做爲節點合併後的新值，不然不爲 NULL 的節點將直接做爲新二叉樹的節點。

示例 1:

輸入: 
	Tree 1                     Tree 2                  
          1                         2                             
         / \                       / \                            
        3   2                     1   3                        
       /                           \   \                      
      5                             4   7                  
輸出: 
合併後的樹:
	     3
	    / \
	   4   5
	  / \   \ 
	 5   4   7

注意: 合併必須從兩個樹的根節點開始。

---

Runtime: 100 ms

Memory Usage: 19.8 MB

 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     func mergeTrees(_ t1: TreeNode?, _ t2: TreeNode?) -> TreeNode? {
16         if t1 == nil {return t2}
17         if t2 == nil {return t1}
18         var t = TreeNode(t1!.val + t2!.val)
19         t.left =  mergeTrees(t1!.left, t2!.left)
20         t.right = mergeTrees(t1!.right, t2!.right)
21         return t
22     }
23 }

---

120ms

 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     func mergeTrees(_ t1: TreeNode?, _ t2: TreeNode?) -> TreeNode? {
16         switch (t1, t2) {
17         case (let t1, nil) where t1 != nil:
18             return t1!
19         case (nil, let t2) where t2 != nil:
20             return t2!
21         case (nil, nil):
22             return nil
23         default:
24             guard let tree1 = t1, let tree2 = t2 else { return nil }
25             let newTree = TreeNode(tree1.val + tree2.val)
26             newTree.left = mergeTrees(tree1.left, tree2.left)
27             newTree.right = mergeTrees(tree1.right, tree2.right)
28             return newTree
29         }
30     }
31 }

---

124ms

 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     func mergeTrees(_ t1: TreeNode?, _ t2: TreeNode?) -> TreeNode? {        
16         guard let t1 = t1 else {
17             return t2
18         }
19         
20         guard let t2 = t2 else {
21             return t1
22         }
23         
24         t1.val += t2.val
25         t1.left = mergeTrees(t1.left, t2.left)
26         t1.right = mergeTrees(t1.right, t2.right)
27         return t1
28     }        
29 }

---

136ms

 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     func mergeTrees(_ t1: TreeNode?, _ t2: TreeNode?) -> TreeNode? {
16             if t1 == nil && t2 == nil { return nil }
17             var newNode = TreeNode((t1?.val ?? 0) + (t2?.val ?? 0))
18 
19             if t1?.left == nil || t2?.left == nil {
20                 newNode.left = t1?.left ?? t2?.left                    
21             } else {
22                 newNode.left = mergeTrees(t1?.left, t2?.left)
23             }
24             
25             if t1?.right == nil || t2?.right == nil {
26                 newNode.right = t1?.right ?? t2?.right                    
27             } else {
28                 newNode.right = mergeTrees(t1?.right, t2?.right)
29             }
30             
31             return newNode
32     }
33 }

---

160ms

 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     func mergeTrees(_ t1: TreeNode?, _ t2: TreeNode?) -> TreeNode? {
16     switch (t1, t2) {
17     case (nil, _): return t2
18     case (_, nil): return t1
19         default:
20             var treeNode: TreeNode
21             treeNode = TreeNode(t1!.val + t2!.val)
22             treeNode.left = mergeTrees(t1!.left, t2!.left)
23             treeNode.right = mergeTrees(t1!.right, t2!.right)
24             return treeNode
25         }
26     }
27 }

---

204ms

 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 A = TreeNode(0)
16     func mergeTrees(_ t1: TreeNode?, _ t2: TreeNode?) -> TreeNode? {
17         if t1 == nil && t2 == nil{
18             return t1
19         }else{
20             B(t1,t2,A)
21         }
22         
23         return A
24     }
25     func B(_ t1: TreeNode?, _ t2: TreeNode?, _ t3: TreeNode?)
26     {
27         if t1?.left != nil && t2?.left != nil
28         {
29             t3?.left = TreeNode(0)
30             B(t1?.left,t2?.left,t3?.left)
31         }else if t1?.left == nil && t2?.left != nil{
32             t3?.left = TreeNode(0)
33             B(nil,t2?.left,t3?.left)
34         }else if t1?.left != nil && t2?.left == nil{
35             t3?.left = TreeNode(0)
36             B(t1?.left,nil,t3?.left)
37         }
38         
39         if t1 != nil && t2 != nil
40         {
41             let a:Int = t1?.val as! Int
42             let b:Int = t2?.val as! Int
43             t3?.val = a + b
44         }else if t1 == nil && t2 != nil{
45             let b:Int = t2?.val as! Int
46             t3?.val = b
47         }else if t1 != nil && t2 == nil{
48             let a:Int = t1?.val as! Int
49             t3?.val = a
50         }else{
51             return
52         }
53         
54         if t1?.right != nil && t2?.right != nil
55         {
56             t3?.right = TreeNode(0)
57             B(t1?.right,t2?.right,t3?.right)
58         }else if t1?.right == nil && t2?.right != nil{
59             t3?.right = TreeNode(0)
60             B(nil,t2?.right,t3?.right)
61         }else if t1?.right != nil && t2?.right == nil{
62             t3?.right = TreeNode(0)
63             B(t1?.right,nil,t3?.right)
64         }else{
65             return
66         }        
67     }
68 }