Serialize and Deserialize BST

题目介绍

LeetCode 449. Serialize and Deserialize BST。

复杂度

时间复杂度: O(n), 空间复杂度: O(n)

解题思路

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 Codec {
    // Encodes a tree to a single string.
    func serialize(_ root: TreeNode?) -> String {
        guard let root = root else {
            return ""
        }
        let (l, r) = (serialize(root.left), serialize(root.right))
        return [String(root.val), l, r].filter { !$0.isEmpty }.joined(separator: " ")
    }

    // Decodes your encoded data to tree.
    func deserialize(_ data: String) -> TreeNode? {
        let vals = data.split(separator: " ").map { Int($0)! }
        var i = 0
        func h(_ cap: Int) -> TreeNode? {
            guard i < vals.count && vals[i] <= cap else {
                return nil
            }
            let root = TreeNode(vals[i])
            i += 1
            root.left = h(root.val)
            root.right = h(cap)
            return root
        }
        return h(Int.max)
    }
}

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