evaluator

fundamentals/math_evaluator/evaluator.go

@@ -0,0 +1,47 @@
+package mathevaluator
+
+import (
+	"math"
+	"strconv"
+	"strings"
+
+	"github.com/fotonmoton/algorithms/fundamentals/stack"
+)
+
+// Dijkstra's two stack algorithm for equation evaluation
+func Evaluate(exression string) int {
+	operations := stack.NewStack()
+	values := stack.NewStack()
+
+	for _, part := range strings.Split(exression, " ") {
+		isOperation := part == "+" || part == "-" || part == "*" || part == "/" || part == "sqrt"
+
+		if part == "(" {
+			continue
+		} else if part == ")" {
+			lastOperation := operations.Pop()
+			lastValue := values.Pop().(int)
+
+			switch lastOperation {
+			case "+":
+				lastValue = values.Pop().(int) + lastValue
+			case "-":
+				lastValue = values.Pop().(int) - lastValue
+			case "*":
+				lastValue = values.Pop().(int) * lastValue
+			case "/":
+				lastValue = values.Pop().(int) / lastValue
+			case "sqrt":
+				lastValue = int(math.Sqrt(float64(lastValue)))
+			}
+			values.Push(lastValue)
+		} else if isOperation {
+			operations.Push(part)
+		} else {
+			newValue, _ := strconv.Atoi(part)
+			values.Push(newValue)
+		}
+	}
+
+	return values.Pop().(int)
+}

fundamentals/math_evaluator/evaluator_test.go

@@ -0,0 +1,30 @@
+package mathevaluator
+
+import (
+	"log"
+	"testing"
+)
+
+func TestSimple(t *testing.T) {
+	result := Evaluate("( 1 + 1 )")
+
+	if result != 2 {
+		log.Fatalf("wrong answer: %v", result)
+	}
+}
+
+func TestSqrt(t *testing.T) {
+	result := Evaluate("sqrt ( 9 )")
+
+	if result != 3 {
+		log.Fatalf("wrong answer: %v", result)
+	}
+}
+
+func TestComplex(t *testing.T) {
+	result := Evaluate("( ( 1 + ( 2 - ( 3 * ( 4 / ( 1 + 1 ) ) ) ) ) + sqrt ( 9 ) )")
+
+	if result != 0 {
+		log.Fatalf("wrong answer: %v", result)
+	}
+}