Advent of Code (Go): solve 2025/06

Author: IsaacG

advent_of_code.go/y2025/06.go

@@ -0,0 +1,85 @@
+package y2025
+
+import (
+	"isaacgood.com/aoc/helpers"
+	"strings"
+)
+
+// Day06 solves 2025/06.
+type Day06 struct {
+	op      map[string]func(int, int) int
+	initial map[string]int
+}
+
+// Solve returns the solution for one part.
+func (p *Day06) Solve(data string, part int) string {
+	p.op = map[string]func(int, int) int{
+		"+": func(a, b int) int { return a + b },
+		"*": func(a, b int) int { return a * b },
+	}
+	p.initial = map[string]int{
+		"+": 0,
+		"*": 1,
+	}
+	return []func(string) string{p.p1, p.p2}[part-1](data)
+}
+
+func (p *Day06) p1(data string) string {
+	lines := helpers.ParseMultiWordsPerLine(data)
+	maxLine := len(lines) - 1
+	var total int
+	for col := range len(lines[0]) {
+		tally := p.initial[lines[maxLine][col]]
+		op := p.op[lines[maxLine][col]]
+		for _, line := range lines[:maxLine] {
+			tally = op(tally, helpers.Atoi(line[col]))
+		}
+		total += tally
+	}
+	return helpers.Itoa(total)
+}
+
+func (p *Day06) p2(data string) string {
+	lines := strings.Split(data, "\n")
+	maxLine := len(lines) - 1
+
+	var colStarts []int
+	var operators []string
+	for idx, char := range lines[len(lines)-1] {
+		if char != ' ' {
+			operators = append(operators, string(char))
+			colStarts = append(colStarts, idx)
+		}
+	}
+
+	var longest int
+	for _, line := range lines {
+		if l := len(line); l > longest {
+			longest = l
+		}
+	}
+	colEnds := colStarts[1:]
+	colEnds = append(colEnds, longest+1)
+
+	var total int
+	for idx, opChar := range operators {
+		tally := p.initial[opChar]
+		op := p.op[opChar]
+
+		for col := colStarts[idx]; col < colEnds[idx]-1; col++ {
+			var number []byte
+			for _, line := range lines[:maxLine] {
+				if char := line[col]; char != ' ' {
+					number = append(number, line[col])
+				}
+			}
+			tally = op(tally, helpers.Atoi(string(number)))
+		}
+		total += tally
+	}
+	return helpers.Itoa(total)
+}
+
+func init() {
+	helpers.AocRegister(2025, 6, &Day06{})
+}