advent-of-code-2024/go/question7/main.go

package main

import (
	"fmt"
	"strconv"
	"strings"
)

const mockInput = "190: 10 19\n3267: 81 40 27\n83: 17 5\n156: 15 6\n7290: 6 8 6 15\n161011: 16 10 13\n192: 17 8 14\n21037: 9 7 18 13\n292: 11 6 16 20"

type ProblemRow struct {
	res     int
	numbers []int
}

func parseRow(s string) *ProblemRow {
	colonIdx := strings.Index(s, ":")
	res, _ := strconv.Atoi(s[0:colonIdx])
	numbers := toSliceOfInt(strings.Split(s[colonIdx+2:], " "))

	return &ProblemRow{res, numbers}
}

func parseProblemInput(input string) []*ProblemRow {
	ret := make([]*ProblemRow, 0)
	for _, row := range strings.Split(input, "\n") {
		ret = append(ret, parseRow(row))
	}
	return ret
}

func toSliceOfInt(split []string) []int {
	ret := make([]int, len(split))
	for i := 0; i < len(split); i++ {
		ret[i], _ = strconv.Atoi(split[i])
	}
	return ret
}

type Operand int8

const (
	PRODUCT Operand = iota
	SUM
	CONCAT
)

type OperandNode struct {
	value    Operand
	nextNode *NumberNode
}

func (n *OperandNode) String() string {
	opp := "+"
	if n.value == PRODUCT {
		opp = "*"
	}
	if n.value == CONCAT {
		opp = "||"
	}
	return fmt.Sprintf("%s %s", opp, n.nextNode.String())
}

type NumberNode struct {
	value    int
	nextNode *OperandNode
}

func (n *NumberNode) String() string {
	rest := ""
	if n.nextNode != nil {
		rest = n.nextNode.String()
	}
	return fmt.Sprintf("%d %s", n.value, rest)
}

func process(node *NumberNode) int {
	if node.nextNode == nil {
		return node.value
	}
	if node.nextNode.value == SUM {
		newValue := node.value + node.nextNode.nextNode.value
		nextNext := node.nextNode.nextNode.nextNode
		newNode := &NumberNode{newValue, nextNext}
		return process(newNode)
	}
	if node.nextNode.value == PRODUCT {
		newValue := node.value * node.nextNode.nextNode.value
		nextNext := node.nextNode.nextNode.nextNode
		newNode := &NumberNode{newValue, nextNext}
		return process(newNode)
	}

	if node.nextNode.value == CONCAT {
		newValue := concatInts(node.value, node.nextNode.nextNode.value)
		nextNext := node.nextNode.nextNode.nextNode
		newNode := &NumberNode{newValue, nextNext}
		return process(newNode)
	}

	panic("Unknown Operand")
}

func concatInts(value, value2 int) int {
	n := 1
	for n <= value2 {
		n = n * 10
	}
	return value2 + n*value

}

func createNodes(numbers []int, operands []Operand) *NumberNode {
	if len(numbers)-1 != len(operands) {
		panic("Number of operands must be 1 minus number of numbers")
	}
	var firstVNode *NumberNode = nil
	var previousONode *OperandNode = nil
	for i := 0; i < len(operands); i++ {
		oNode := &OperandNode{operands[i], nil}
		vNode := &NumberNode{numbers[i], oNode}
		if firstVNode == nil {
			firstVNode = vNode
		}
		if previousONode != nil {
			previousONode.nextNode = vNode
		}
		previousONode = oNode
	}
	previousONode.nextNode = &NumberNode{numbers[len(numbers)-1], nil}
	return firstVNode
}

func createAllPossibleChain(numbers []int, operands ...Operand) <-chan *NumberNode {
	out := make(chan *NumberNode)
	go func() {
		for operators := range allPossibleOperators(len(numbers)-1, operands...) {
			out <- createNodes(numbers, operators)
		}
		close(out)
	}()
	return out
}

func allPossibleOperators(n int, operands ...Operand) <-chan []Operand {
	out := make(chan []Operand)
	go func() {
		defer close(out)
		if n == 0 {
			out <- []Operand{}
			return
		}
		for _, operand := range operands {
			for prefix := range allPossibleOperators(n-1, operands...) {
				out <- append(prefix, operand)
			}
		}
	}()
	return out
}

func problem7A(input string) int {
	ret := 0
	for _, problemRow := range parseProblemInput(input) {
		if isSolvable(problemRow, SUM, PRODUCT) {
			ret += problemRow.res
		}
	}
	return ret
}

func problem7B(input string) int64 {
	var ret int64 = 0
	for _, problemRow := range parseProblemInput(input) {
		if isSolvable(problemRow, PRODUCT, SUM, CONCAT) {
			ret += int64(problemRow.res)
		}
	}
	return ret
}

func isSolvable(row *ProblemRow, operands ...Operand) bool {
	for node := range createAllPossibleChain(row.numbers, operands...) {
		if process(node) == row.res {
			return true
		}
	}
	return false
}

func main() {

	fmt.Printf("The answer to question 7A is %d \n", problem7A(realInput))
	fmt.Printf("The answer to question 7B is %d \n", problem7B(realInput))

}