From 81075f89203ad8d58012720595a663b23ef895f3 Mon Sep 17 00:00:00 2001
From: Gabriel Augendre <gabriel@augendre.info>
Date: Thu, 12 Aug 2021 18:08:33 +0200
Subject: [PATCH] Add equivalent resistor

---
 training/equivalent_resistor.go | 92 +++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 training/equivalent_resistor.go

diff --git a/training/equivalent_resistor.go b/training/equivalent_resistor.go
new file mode 100644
index 0000000..8c9e3cf
--- /dev/null
+++ b/training/equivalent_resistor.go
@@ -0,0 +1,92 @@
+package main
+
+import "fmt"
+import "os"
+import "bufio"
+import "strings"
+
+const VALUE = "value"
+const SERIES = "series"
+const PARALLEL = "parallel"
+
+type Operation struct {
+	operator string
+	value    int
+	operands []*Operation
+	parent   *Operation
+}
+
+func (op *Operation) addOperand(other *Operation) {
+	op.operands = append(op.operands, other)
+}
+
+func (op *Operation) setOperator(diagramItem string) {
+	if diagramItem == "[" {
+		op.operator = PARALLEL
+	} else if diagramItem == "(" {
+		op.operator = SERIES
+	}
+}
+
+func (op *Operation) compute() float64 {
+	if op.operator == VALUE {
+		return float64(op.value)
+	}
+	var operandValues []float64
+	for _, operation := range op.operands {
+		operandValues = append(operandValues, operation.compute())
+	}
+	sum := 0.0
+	if op.operator == SERIES {
+		for _, value := range operandValues {
+			sum += value
+		}
+	} else {
+		for _, value := range operandValues {
+			sum += 1 / value
+		}
+		sum = 1 / sum
+	}
+	return sum
+}
+
+func main() {
+	scanner := bufio.NewScanner(os.Stdin)
+	scanner.Buffer(make([]byte, 1000000), 1000000)
+
+	var N int
+	scanner.Scan()
+	fmt.Sscan(scanner.Text(), &N)
+
+	resistors := make(map[string]int)
+	for i := 0; i < N; i++ {
+		var name string
+		var R int
+		scanner.Scan()
+		fmt.Sscan(scanner.Text(), &name, &R)
+		resistors[name] = R
+	}
+	scanner.Scan()
+	circuit := strings.Split(scanner.Text(), " ")
+	mainOperation := &Operation{}
+	mainOperation.setOperator(circuit[0])
+	currentOperation := mainOperation
+	for _, item := range circuit[1:] {
+		if item == "[" || item == "(" {
+			newOp := &Operation{parent: currentOperation}
+			currentOperation = newOp
+			currentOperation.setOperator(item)
+		} else if item == "]" || item == ")" {
+			if currentOperation != mainOperation {
+				currentOperation.parent.addOperand(currentOperation)
+				currentOperation = currentOperation.parent
+			}
+		} else {
+			value := resistors[item]
+			valueOp := &Operation{operator: VALUE, value: value, parent: currentOperation}
+			currentOperation.addOperand(valueOp)
+		}
+	}
+
+	fmt.Printf("%.1f\n", mainOperation.compute())
+}