add exercise of equations

src/main/kotlin/it/norangeb/algorithms/exam/Equations.kt

@@ -0,0 +1,73 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2019 norangebit
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+
+package it.norangeb.algorithms.exam
+
+import java.lang.Exception
+import java.util.Stack
+
+object Equations {
+    fun compute(equation: String): Double {
+        val operator = Stack<Operations>()
+        val operandi = Stack<Double>()
+
+        equation.split(" ").forEach {
+            when (it) {
+                "+" -> operator.push(Operations.PLUS)
+                "-" -> operator.push(Operations.MINUS)
+                "*" -> operator.push(Operations.PER)
+                ")" -> operandi.push(
+                    canculate(operator.pop(), operandi.pop(), operandi.pop())
+                )
+                else -> {
+                    try {
+                        operandi.push(it.toDouble())
+                    } catch (e: Exception) {
+                        println("error, $e")
+                    }
+                }
+            }
+        }
+
+        return operandi.pop()
+    }
+
+    private fun canculate(
+        op: Operations,
+        d1: Double,
+        d2: Double
+    ): Double {
+        println("$d1, $op, $d2")
+        return when (op) {
+            Operations.PLUS -> d1 + d2
+            Operations.MINUS -> d2 - d1
+            Operations.PER -> d1 * d2
+        }
+    }
+}
+
+enum class Operations {
+    PLUS, MINUS, PER
+}

src/test/kotlin/it/norangeb/algorithms/exam/EquationsTest.kt

@@ -0,0 +1,56 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2019 norangebit
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+
+package it.norangeb.algorithms.exam
+
+import org.amshove.kluent.`should be equal to`
+import org.spekframework.spek2.Spek
+import org.spekframework.spek2.style.gherkin.Feature
+
+object EquationsTest : Spek({
+    Feature("equations") {
+        Scenario("equations") {
+            val calculator by memoized { Equations }
+
+            var result: Double = 0.0
+
+            When("compute 2 + 3 * ( 3 - 1 )") {
+                result = calculator.compute("( 2 + ( 3  * ( 3 - 1 ) ) )")
+            }
+
+            Then("result should equal 8") {
+                result `should be equal to` 8.0
+            }
+
+            When("compute (((1 + 2) * (2 + 3)) + 1) * ( 3 - 1 )") {
+                result = calculator.compute("( ( ( ( 1 + 2 ) * ( 2 + 3 ) ) + 1 ) * ( 3 - 1 ) )")
+            }
+
+            Then("result should equal 32") {
+                result `should be equal to` 32.0
+            }
+        }
+    }
+})