Map (Dictionary) trong Kotlin

fun main() {
    val ages = mapOf(
        "Alice" to 25,
        "Bob" to 30,
        "Charlie" to 35
    )
    
    println(ages["Alice"])  // 25
    println(ages.size)      // 3
}

fun main() {
    val ages = mutableMapOf("Alice" to 25)
    
    // Thêm
    ages["Bob"] = 30
    ages.put("Charlie", 35)
    ages.putAll(mapOf("Dan" to 40, "Eve" to 28))
    
    // Xóa
    ages.remove("Bob")
    
    println(ages)
}

fun main() {
    val map = mapOf("a" to 1, "b" to 2, "c" to 3)
    
    println(map["a"])              // 1
    println(map["z"])              // null
    println(map.getOrDefault("z", 0))  // 0
    println(map.getOrElse("z") { -1 }) // -1
    
    // Keys và values
    println(map.keys)    // [a, b, c]
    println(map.values)  // [1, 2, 3]
}

fun main() {
    val map = mapOf("a" to 1, "b" to 2)
    
    println(map.containsKey("a"))    // true
    println("a" in map)               // true
    println(map.containsValue(2))    // true
    println(map.isEmpty())           // false
}

fun main() {
    val map = mapOf("a" to 1, "b" to 2, "c" to 3)
    
    // Duyệt entries
    for ((key, value) in map) {
        println("$key -> $value")
    }
    
    // forEach
    map.forEach { (k, v) -> println("$k: $v") }
    
    // Duyệt keys
    for (key in map.keys) {
        println(key)
    }
}

fun main() {
    val ages = mapOf("Alice" to 25, "Bob" to 30, "Charlie" to 20)
    
    // Filter
    val adults = ages.filter { (_, age) -> age >= 25 }
    println(adults)  // {Alice=25, Bob=30}
    
    // filterKeys / filterValues
    val short = ages.filterKeys { it.length <= 3 }
    val young = ages.filterValues { it < 25 }
    
    // Map values
    val doubled = ages.mapValues { (_, v) -> v * 2 }
    println(doubled)  // {Alice=50, Bob=60, Charlie=40}
    
    // Map keys
    val upper = ages.mapKeys { (k, _) -> k.uppercase() }
}

fun main() {
    val map1 = mapOf("a" to 1, "b" to 2)
    val map2 = mapOf("b" to 3, "c" to 4)
    
    // Plus - map2 ghi đè map1
    val merged = map1 + map2
    println(merged)  // {a=1, b=3, c=4}
    
    // Minus
    val removed = map1 - "a"
    println(removed)  // {b=2}
}

fun main() {
    // HashMap - không đảm bảo thứ tự
    val hashMap = hashMapOf("a" to 1)
    
    // LinkedHashMap - giữ thứ tự thêm vào
    val linkedMap = linkedMapOf("a" to 1, "b" to 2)
    
    // SortedMap - sắp xếp theo key
    val sortedMap = sortedMapOf("c" to 3, "a" to 1, "b" to 2)
    println(sortedMap)  // {a=1, b=2, c=3}
}

fun main() {
    // Đếm tần suất
    val words = listOf("apple", "banana", "apple", "cherry", "banana", "apple")
    val frequency = mutableMapOf<String, Int>()
    
    for (word in words) {
        frequency[word] = frequency.getOrDefault(word, 0) + 1
    }
    println(frequency)  // {apple=3, banana=2, cherry=1}
    
    // Grouping
    data class Person(val name: String, val city: String)
    val people = listOf(
        Person("Alice", "NYC"),
        Person("Bob", "LA"),
        Person("Charlie", "NYC")
    )
    val byCity = people.groupBy { it.city }
    println(byCity)
}