2023 Day 9 Complete!

2023/day09/main.go

@@ -0,0 +1,110 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+// 2185006187 is too high
+// 1920491799 is too high
+
+func main() {
+	inp := h.StdinToStringSlice()
+	solve(inp)
+}
+
+func solve(input []string) {
+	var p1result, p2result int
+	for i := range input {
+		s := NewSeq(i, input[i])
+		s.stabilize()
+		s.predict()
+		v2, v1 := s.value()
+		p1result += v1
+		p2result += v2
+	}
+	fmt.Println("# Part 1")
+	fmt.Println(p1result)
+	fmt.Println()
+	fmt.Println("# Part 2")
+	fmt.Println(p2result)
+}
+
+type Seq struct {
+	row     int
+	history [][]int
+}
+
+func NewSeq(row int, input string) *Seq {
+	s := Seq{row: row}
+	pts := strings.Fields(input)
+	first := []int{}
+	for i := range pts {
+		first = append(first, h.Atoi(pts[i]))
+	}
+	s.history = append(s.history, first)
+	return &s
+}
+
+func (s *Seq) value() (int, int) {
+	return s.history[0][0], s.history[0][len(s.history[0])-1]
+}
+func (s *Seq) predict() {
+	s.history[len(s.history)-1] = append(s.history[len(s.history)-1], 0)
+	s.history[len(s.history)-1] = append([]int{0}, s.history[len(s.history)-1]...)
+	if len(s.history) > 1 {
+		for i := len(s.history) - 2; i >= 0; i-- {
+			nV := s.history[i][len(s.history[i])-1] + s.history[i+1][len(s.history[i+1])-1]
+			s.history[i] = append(s.history[i], nV)
+
+			// And now go backwards
+			pV := s.history[i][0] - s.history[i+1][0]
+			s.history[i] = append([]int{pV}, s.history[i]...)
+		}
+	}
+}
+
+func (s *Seq) stabilize() {
+	for !s.isStable() {
+		s.iterate()
+	}
+}
+
+func (s *Seq) iterate() {
+	idx := len(s.history) - 1
+	l := len(s.history[idx]) - 1
+	var next []int
+	for i := range s.history[idx] {
+		if i < l {
+			next = append(next, s.history[idx][i+1]-s.history[idx][i])
+		}
+	}
+	s.history = append(s.history, next)
+}
+
+func (s *Seq) isStable() bool {
+	for _, v := range s.history[len(s.history)-1] {
+		if v != 0 {
+			return false
+		}
+	}
+	return true
+}
+
+func (s Seq) String() string {
+	return fmt.Sprintf("MINE: Row %d Result: %d + %d = %d\n",
+		s.row,
+		s.history[0][len(s.history[0])-2],
+		s.history[1][len(s.history[1])-1],
+		s.history[0][len(s.history[0])-1])
+}
+
+func (s Seq) Detail() string {
+	var res string
+	for i := range s.history {
+		res = fmt.Sprintf("%s%v\n", res, s.history[i])
+	}
+	return res
+}