package main

import (
    "os"
    "fmt"
    "strings"
    "strconv"
    "math"
)

// data types
type Equation struct {
    result int
    params []int
}

// general util
func check(e error) {
    if e != nil { panic(e) }
}

func newEquations(data string) []*Equation {
    /* Reads the puzzle input, return a list of Equation structs.
     */
    lines := strings.Split(data, "\n")
    equations := make([]*Equation, 0, len(lines))

    for _, line := range lines {
        split_line := strings.Split(line, ":")
        
        // get result/ number before the colon
        result, err := strconv.Atoi(split_line[0])
        check(err)
        
        // parse paramter/ numbers after the colon
        str_params := strings.Split(strings.TrimSpace(split_line[1]), " ")
        params := make([]int, 0, len(str_params))
        for _, num := range str_params {
            param, err := strconv.Atoi(num)
            check(err)

            params = append(params, param)
        }

        equations = append(equations, &Equation{ result: result, params: params })
    }

    return equations
}

func incr(arr []int) []int {
    /* least significant bit first increment, base 3 */
    over := 1
    for i := range arr {
        if over == 0 { break }  
        arr[i] += over
        over   = arr[i] / 3
        arr[i] = arr[i] % 3
    }
    return arr
}

func isValid(eq *Equation) bool {
    /* Checks whether the equation could be right by combining the paramters in
     * all possible ways and comparing to the result.
     */

    operators := make([]int, len(eq.params) - 1)

    for range int(math.Pow(3.0, float64(len(operators)))) {

        // calc possible result
        acc := eq.params[0]
        for i, op := range operators {
            if op == 0 {
                acc += eq.params[i + 1]
            } else if op == 1 {
                acc *= eq.params[i + 1]
            } else if op == 2 {
                num, err := strconv.Atoi(strconv.Itoa(acc) + strconv.Itoa(eq.params[i + 1]))
                check(err)
                acc = num
            }
        }

        // compare to actual result
        if acc == eq.result { return true }

        operators = incr(operators)
    }
    return false
}

// main loop
func main() {

    // read in file
    dat, err := os.ReadFile("data.txt")
    check(err)
    dat_str := strings.TrimSpace(string(dat))
    

    equations := newEquations(dat_str)

    result := 0
    for _, eq := range equations {
        if isValid(eq) { result += eq.result }
    }

    fmt.Println(result)
}