Map (Dictionary) trong Kotlin

val capitals = mapOf(
    "Vietnam" to "Hanoi",
    "Japan" to "Tokyo",
    "France" to "Paris"
)
println(capitals["Vietnam"])  // Hanoi

// Immutable
val map = mapOf("a" to 1, "b" to 2)
val empty = emptyMap<String, Int>()
 
// Mutable
val mutableMap = mutableMapOf("a" to 1)
val hashMap = hashMapOf("a" to 1)
val linkedMap = linkedMapOf("a" to 1)  // Giữ thứ tự
val sortedMap = sortedMapOf("b" to 2, "a" to 1)  // Sort by key

val scores = mapOf("Alice" to 95, "Bob" to 87, "Charlie" to 92)
 
// Get
println(scores["Alice"])        // 95
println(scores["Unknown"])      // null
println(scores.getOrDefault("Unknown", 0))  // 0
println(scores.getOrElse("Unknown") { -1 }) // -1
 
// Keys & Values
println(scores.keys)    // [Alice, Bob, Charlie]
println(scores.values)  // [95, 87, 92]
 
// Entries
for ((name, score) in scores) {
    println("$name: $score")
}

val map = mutableMapOf("a" to 1)
 
// Add/Update
map["b"] = 2
map.put("c", 3)
map += "d" to 4
map.putAll(mapOf("e" to 5, "f" to 6))
 
// Remove
map.remove("a")
map -= "b"
 
// Compute
map.compute("c") { _, v -> (v ?: 0) + 10 }
map.getOrPut("g") { 7 }  // Add if not exists

val scores = mapOf("Alice" to 95, "Bob" to 87)
 
// Map values
val doubled = scores.mapValues { (_, v) -> v * 2 }
 
// Map keys
val lowercase = scores.mapKeys { (k, _) -> k.lowercase() }
 
// Filter
val high = scores.filter { (_, v) -> v >= 90 }
 
// To list of pairs
val pairs = scores.toList()  // [(Alice, 95), (Bob, 87)]

fun main() {
    val words = "hello world hello kotlin world kotlin kotlin"
    
    // TODO: Đếm tần suất xuất hiện của mỗi từ
}

fun main() {
    val words = "hello world hello kotlin world kotlin kotlin"
    
    val frequency = words.split(" ")
        .groupingBy { it }
        .eachCount()
    
    println(frequency)  // {hello=2, world=2, kotlin=3}
    
    val mostCommon = frequency.maxByOrNull { it.value }
    println("Most common: ${mostCommon?.key}")  // kotlin
}