[hackerrank] "Fraudulent Activity notifications" N·log(d) 구현

Author: codehumane

src/main/kotlin/hackerrank/sorting/FraudulentActivityNotifications.kt

@@ -0,0 +1,46 @@
+package hackerrank.sorting
+
+fun activityNotifications(expenditure: Array<Int>, d: Int): Int {
+    var count = 0
+
+    (d until expenditure.size).forEach {
+        if (isNotification(expenditure, it, d)) count++
+    }
+
+    return count
+}
+
+fun isNotification(
+    expenditure: Array<Int>,
+    index: Int,
+    range: Int
+): Boolean {
+
+    val median = median(
+        expenditure,
+        index - range,
+        index - 1
+    )
+
+    return expenditure[index].toFloat() >= (median * 2f)
+}
+
+private fun median(
+    source: Array<Int>,
+    from: Int,
+    to: Int
+): Float {
+
+    val copy = source
+        .copyOfRange(from, to + 1)
+        .apply { sort() }
+
+    val mid = copy.size.div(2)
+
+    return if (copy.size.rem(2) == 0) {
+        (copy[mid] + copy[mid + 1]).div(2f)
+    } else {
+        copy[mid].toFloat()
+    }
+
+}

src/test/kotlin/hackerrank/sorting/FraudulentActivityNotificationsKtTest.kt

@@ -0,0 +1,14 @@
+package hackerrank.sorting
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class FraudulentActivityNotificationsKtTest {
+
+    @Test
+    fun activityNotifications() {
+        assertEquals(2, activityNotifications(arrayOf(2, 3, 4, 2, 3, 6, 8, 4, 5), 5))
+        assertEquals(0, activityNotifications(arrayOf(1, 2, 3, 4, 4), 4))
+    }
+
+}