-
Notifications
You must be signed in to change notification settings - Fork 889
/
SymmetricTree.swift
40 lines (36 loc) · 1.05 KB
/
SymmetricTree.swift
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
/**
* Question Link: https://leetcode.com/problems/symmetric-tree/
* Primary idea: recursion
* Time Complexity: O(n), Space Complexity: O(n)
*
* Definition for a binary tree node.
* 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 SymmetricTree {
func isSymmetric(_ root: TreeNode?) -> Bool {
guard let root = root else {
return true
}
return isSymmetricHelper(root.left, root.right)
}
private func isSymmetricHelper(_ left: TreeNode?, _ right: TreeNode?) -> Bool {
if left == nil && right == nil {
return true
}
if let left = left, let right = right, left.val == right.val {
return isSymmetricHelper(left.left, right.right) && isSymmetricHelper(left.right, right.left)
} else {
return false
}
}
}