Serialize and Deserialize Binary Tree

题目介绍

LeetCode 297. Serialize and Deserialize Binary Tree。

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 {
    private static let spliter = ","
    private static let nullStr = "N"

    func serialize(_ root: TreeNode?) -> String {
        var str = ""
        buildString(root, &str)
        return str
    }

    private func buildString(_ root: TreeNode?, _ str: inout String) {
        guard let root = root else {
            str = str + Codec.nullStr + Codec.spliter
            return
        }
        str = str + "\(root.val)" + Codec.spliter
        buildString(root.left, &str)
        buildString(root.right, &str)
    }

    func deserialize(_ data: String) -> TreeNode? {
        var nodes: [String] = data.split(separator: Character(Codec.spliter)).map { String($0) }
        return buildTree(&nodes)
    }

    private func buildTree(_ nodes: inout [String]) -> TreeNode? {
        let val = nodes.removeFirst()
        if val == Codec.nullStr {
            return nil
        }
        let node = TreeNode(Int(val)!)
        node.left = buildTree(&nodes)
        node.right = buildTree(&nodes)
        return node
    }
}

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