1 files changed, 119 insertions, 0 deletions
diff --git a/src/PatternFinder.kt b/src/PatternFinder.kt
new file mode 100644
index 0000000..bbab9ae
--- /dev/null
+++ b/src/PatternFinder.kt
@@ -0,0 +1,119 @@
+import java.lang.Math.floor
+import java.lang.Math.max
+import javax.script.ScriptEngine
+import javax.script.ScriptEngineManager
+
+data class Expression(val expression: String)
+
+fun main(args:Array<String>) {
+    while (true) {
+        println("---------------------------")
+        println("Separate numbers by comma.")
+        print("Enter numbers: ")
+
+        val inputNumbers = readLine()!!.split(",").map { it.trim().toDouble() }
+        val formula = findFormula(inputNumbers)
+        println("Formula: $formula")
+        println("Pattern: " + continuePattern(formula))
+    }
+}
+
+private fun findFormula(numbers: List<Double>): String {
+    // Find difference between numbers
+    val differences = listOf(
+            numbers[1] - numbers[0],
+            numbers[2] - numbers[1]
+    )
+
+    var incrementsByDifference = true
+    var increment = 0.0
+    if (differences[0] != differences[1]) // If the pattern doesn't increment by difference
+        incrementsByDifference = false
+    else
+        increment = differences[0]
+
+    // Start-value
+    val nAsExponent = nAsExponent(differences)
+    val startValueDifference = when {
+        incrementsByDifference -> differences[0]             // xn
+        nAsExponent            -> getBase(differences) // x^n
+        else                   -> 1.0                        // n^x
+    }
+
+    val startValue = numbers[0] - startValueDifference
+
+    // Exponents
+    var base = "n"
+    var exponent = ""
+    if (nAsExponent(differences)) {
+        base = getBase(differences).cleanRedundancy() + "^"
+        exponent = "n"
+    } else if (!incrementsByDifference) {
+        base = "n^"
+        exponent = getExponent(numbers[1], startValue).cleanRedundancy()
+    }
+
+    // Add the pieces together
+    var formula = increment.cleanRedundancy()
+    formula += base + exponent + startValue.cleanRedundancy().addSign()
+
+    return formula
+}
+
+private fun continuePattern(formula: String): String {
+    var output = ""
+    for (i in 1..20) {
+        val expression = Expression(formula.replace("n", i.toString()))
+        output += expression.calculate().cleanRedundancy() + ", "
+    }
+
+    return output.cleanRedundancy()
+}
+
+fun Double.cleanRedundancy(): String {
+    return when {
+        this == 0.0         -> return ""
+        floor(this) == this -> this.toInt().toString()
+        else                -> return this.toString()
+    }
+}
+
+fun String.cleanRedundancy(): String {
+    return if (this.endsWith(", "))
+        this.substring(0, this.length - 3)
+    else
+        this
+}
+
+fun String.addSign(): String {
+    return if (!this.startsWith("-"))
+        "+" + this
+    else
+        this
+}
+
+fun Expression.calculate(): Double {
+    val addSubSign = max(expression.indexOf("+"), expression.indexOf("-"))
+    val addSub = expression.substring(addSubSign + 1, expression.length).toDouble()
+    val numbers = expression.substring(0, addSubSign)
+            .split(Regex("[*^]")).map { it.toDouble() }
+
+    if (expression.contains("*"))
+        return numbers[0] * numbers[1] + addSub
+    else if (expression.contains("^"))
+        return Math.pow(numbers[0], numbers[1]) + addSub
+    return 0.0
+}
+
+private fun getBase(differences: List<Double>): Double {
+    return differences[1] / differences[0]
+}
+
+private fun getExponent(secondNumber: Double, startValue: Double): Double {
+    return Math.log(secondNumber - startValue) / Math.log(2.0)
+}
+
+private fun nAsExponent(differences: List<Double>): Boolean {
+    val base = getBase(differences)
+    return  base == differences[0] / (differences[0] / base)
+}
+\ No newline at end of file