字典（Dict）

let capitals = ["France": "Paris", "Italy": "Rome", "Japan": "Tokyo"]

// 获取值（返回可选类型）
if let paris = capitals["France"] {
    print("法国的首都是 \(paris)") // 输出: 法国的首都是 Paris
}

// 获取不存在的键
let london = capitals["UK"] // london 为 nil

// 提供默认值
let ukCapital = capitals["UK", default: "London"]
print(ukCapital) // 输出: London

// 计算出现次数
let words = ["apple", "banana", "apple", "orange"]
var wordCounts = [String: Int]()
for word in words {
    wordCounts[word, default: 0] += 1
}
print(wordCounts) // 输出: ["apple": 2, "banana": 1, "orange": 1]

// 查找第一个符合条件的键值对
if let firstCapital = capitals.first(where: { $0.key == "Italy" }) {
    print("意大利的首都是 \(firstCapital.value)") // 输出: 意大利的首都是 Rome
}

// 获取所有键
let countries = capitals.keys
print(countries) // 输出: ["France", "Italy", "Japan"]

// 获取所有值
let cities = capitals.values
print(cities) // 输出: ["Paris", "Rome", "Tokyo"]

// 过滤符合条件的键值对
let asianCountries = capitals.filter { country, capital in
    country == "Japan" || country == "China"
}
print(asianCountries) // 输出: ["Japan": "Tokyo"]

if let italyCapital = capitals["Italy"] {
    print("意大利的首都是 \(italyCapital)")
} else {
    print("未找到意大利的首都信息")
}

let germanyCapital = capitals["Germany"] ?? "Berlin"
print(germanyCapital) // 输出: Berlin

func printCapital(for country: String) {
    guard let capital = capitals[country] else {
        print("未找到 \(country) 的首都信息")
        return
    }
    print("\(country) 的首都是 \(capital)")
}

printCapital(for: "France") // 输出: France 的首都是 Paris
printCapital(for: "Canada") // 输出: 未找到 Canada 的首都信息

let rome = capitals["Italy"]! // 如果键不存在会崩溃

if let rome = capitals["Italy"] {
    // 安全使用
}

// 旧方法
var scores = ["Alice": 5, "Bob": 3]
scores["Alice"] = (scores["Alice"] ?? 0) + 1

// 新方法（Swift 4+）
scores["Alice", default: 0] += 1

// 使用空合运算符
let score = scores["Charlie"] ?? 0

// 使用字典的默认值方法
let defaultValue = scores["Charlie", default: 0]

struct Country {
    var name: String
    var capital: String
}

let countries = [
    "FR": Country(name: "France", capital: "Paris"),
    "IT": Country(name: "Italy", capital: "Rome")
]

// 使用键路径获取值
if let italyCapital = countries["IT"]?.capital {
    print(italyCapital) // 输出: Rome
}

import Foundation

struct CapitalCitySystem {
    private var capitals: [String: String]
    
    init() {
        capitals = [
            "France": "Paris",
            "Italy": "Rome",
            "Japan": "Tokyo",
            "Germany": "Berlin",
            "Spain": "Madrid",
            "China": "Beijing",
            "India": "New Delhi",
            "Brazil": "Brasília",
            "Australia": "Canberra",
            "Canada": "Ottawa"
        ]
    }
    
    func getCapital(for country: String) -> String? {
        capitals[country]
    }
    
    func getCapitalWithDefault(for country: String) -> String {
        capitals[country, default: "未知"]
    }
    
    func searchCapitals(containing searchText: String) -> [String: String] {
        capitals.filter { country, capital in
            country.localizedCaseInsensitiveContains(searchText) ||
            capital.localizedCaseInsensitiveContains(searchText)
        }
    }
    
    mutating func addCapital(country: String, capital: String) {
        capitals[country] = capital
    }
    
    mutating func removeCapital(for country: String) {
        capitals[country] = nil
    }
    
    func printAllCapitals() {
        for (country, capital) in capitals.sorted(by: { $0.key < $1.key }) {
            print("\(country): \(capital)")
        }
    }
}

// 使用示例
var system = CapitalCitySystem()

// 查询首都
if let franceCapital = system.getCapital(for: "France") {
    print("法国的首都是 \(franceCapital)")
}

// 使用默认值查询
let russiaCapital = system.getCapitalWithDefault(for: "Russia")
print("俄罗斯的首都是 \(russiaCapital)") // 输出: 俄罗斯的首都是 未知

// 添加新首都
system.addCapital(country: "Russia", capital: "Moscow")
print(system.getCapital(for: "Russia") ?? "未找到") // 输出: Moscow

// 搜索功能
let searchResults = system.searchCapitals(containing: "a")
print("包含 'a' 的国家/首都:")
for (country, capital) in searchResults {
    print("- \(country): \(capital)")
}

// 删除首都
system.removeCapital(for: "Brazil")
print(system.getCapital(for: "Brazil") ?? "巴西信息已删除") // 输出: 巴西信息已删除

// 打印所有首都
print("\n所有国家及其首都:")
system.printAllCapitals()

var dict1 = ["name": "Alice", "age": 25]
let dict2 = ["age": 30, "city": "New York"]

dict1.merge(dict2) { (_, new) in 
    return new 
}
// dict1 = ["name": "Alice", "age": 30, "city": "New York"]

let dict = ["A": 10, "B": 20, "C": 15, "D": 5]
let filteredDict = dict.filter { $0.value > 10 }
// filteredDict = ["B": 20, "C": 15]

let dict = ["name": "Alice"]
let age = dict["age", default: "Not specified"] // age = "Not specified"

let array = [1, 2, 3, 4, 5, 6]
let grouped = Dictionary(grouping: array, by: { $0 % 2 })
// grouped = [0: [2, 4, 6], 1: [1, 3, 5]]

let dict = ["key1": "123", "key2": "abc", "key3": "456"]
let numberDict = dict.compactMapValues { Int($0) }
// numberDict = ["key1": 123, "key3": 456]

let dict = ["A": 10, "B": 20, "C": 15]
let maxPair = dict.max(by: { $0.value < $1.value }) 
// maxPair = ("B", 20)