add day7

day7/combine_with_concat.go

@@ -0,0 +1,111 @@
+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)
+}