add day 20 sample solution

doesn't work for input

day20.go

@@ -0,0 +1,143 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type Number struct {
+	x    int
+	prev *Number
+	next *Number
+}
+
+const SIZE = 7
+
+func print_sequence(seq []*Number, start int, end int) {
+	now := seq[start]
+	for i := 0; i < SIZE*2; i++ {
+		fmt.Print(now.x, " ")
+		now = now.next
+	}
+	fmt.Println()
+	now = seq[end]
+	for i := 0; i < SIZE*2; i++ {
+		fmt.Print(now.x, " ")
+		now = now.prev
+	}
+	fmt.Println()
+}
+
+func get_value_for_position(seq []*Number, start int, length int) int {
+	now := seq[start]
+	for i := 0; i < length; i++ {
+		now = now.next
+	}
+	return now.x
+}
+
+func main() {
+
+	input, _ := os.ReadFile("./input/input20.txt")
+
+	var sequencia [SIZE]*Number
+	var zero_pos int
+
+	lines := strings.Split(string(input), "\r\n")
+	for i, line := range lines {
+		x, _ := strconv.Atoi(line)
+		if x == 0 {
+			zero_pos = i
+		}
+		sequencia[i] = &Number{x, nil, nil}
+	}
+	for i, _ := range sequencia {
+		prev := i - 1
+		if prev < 0 {
+			prev = SIZE - 1
+		}
+		sequencia[i].next = sequencia[(i+1)%SIZE]
+		sequencia[i].prev = sequencia[prev]
+	}
+
+	for i := 0; i < SIZE; i++ {
+
+		move := sequencia[i].x
+		starting_pos := sequencia[i]
+		new_pos := sequencia[i]
+		before_start := starting_pos.prev
+		after_start := starting_pos.next
+		if move > 0 {
+			for {
+				if move > 0 {
+					new_pos = new_pos.next
+					move--
+				} else {
+					break
+				}
+			}
+			if new_pos == starting_pos {
+				fmt.Println("Edge Case?")
+				continue
+			}
+			if new_pos == starting_pos.prev {
+				fmt.Println("Edge Case?")
+				continue
+			}
+			after_new_pos := new_pos.next
+
+			starting_pos.next = after_new_pos
+			starting_pos.prev = new_pos
+
+			new_pos.next = starting_pos
+			if new_pos.prev == starting_pos {
+				new_pos.prev = before_start
+			}
+
+			after_new_pos.prev = starting_pos
+
+			before_start.next = after_start
+			after_start.prev = before_start
+		} else if move < 0 {
+			move--
+			for {
+				if move < 0 {
+					new_pos = new_pos.prev
+					move++
+				} else {
+					break
+				}
+			}
+			if new_pos == starting_pos {
+				fmt.Println("Edge Case?")
+				continue
+			}
+			if new_pos == starting_pos.prev {
+				fmt.Println("Edge Case?")
+				continue
+			}
+			after_new_pos := new_pos.next
+
+			starting_pos.next = after_new_pos
+			starting_pos.prev = new_pos
+
+			new_pos.next = starting_pos
+
+			after_new_pos.prev = starting_pos
+
+			before_start.next = after_start
+			after_start.prev = before_start
+		}
+	}
+
+	//print_sequence(sequencia[:], 0, 4)
+
+	part1 := get_value_for_position(sequencia[:], zero_pos, 1000)
+	part1 += get_value_for_position(sequencia[:], zero_pos, 2000)
+	part1 += get_value_for_position(sequencia[:], zero_pos, 3000)
+
+	fmt.Println("Part 1:", part1) // 7238 too low // correct according to HAM: 7584
+	fmt.Println("Part 2:", 0)
+}

input/input20.txt

@@ -0,0 +1,7 @@
+1
+2
+-3
+3
+-2
+0
+4