day 12,13

2023/go/day13/day13.go

@@ -0,0 +1,144 @@
+package day13
+
+import (
+	"adventofcode2023/utils"
+	"fmt"
+	"strings"
+)
+
+type mirrorLoc struct {
+	orient string
+	index int
+}
+func Part1(input string) int {
+	count := 0
+
+	patterns := strings.Split(input, "\n\n")
+	for p, pattern := range patterns {
+		rows := strings.Split(pattern, "\n")
+		if v, ok := findMirror(rows); ok {
+			count = count + v * 100
+		} else {
+			cols := swap(rows)
+			if v, ok := findMirror(cols); ok {
+				count = count + v
+			} else {
+				utils.PanicOnErr(fmt.Errorf("p: %v\n %v\n", p, pattern))
+			}
+		}
+	}
+	return count
+}
+
+func Part2(input string) int {
+	count := 0
+	patterns := strings.Split(input, "\n\n")
+
+	for p, pattern := range patterns {
+		rows := strings.Split(pattern, "\n")
+		loc, _ := findMirrorLoc(rows)
+		found := false
+		for i:=0;i<len(rows[0])*len(rows);i++{
+			newRows := smudge(i, rows)
+			if v, ok := findNewMirrorLoc(loc, newRows); ok {
+				if v != loc {
+					found = true
+					if v.orient == "row" {
+						count = count + v.index * 100
+					} else {
+						count = count + v.index
+					}
+					break
+				}
+			}
+		}
+		if ! found {
+			utils.PanicOnErr(fmt.Errorf("p: %v\n %v\n", p, pattern))
+		}
+	}
+	return count
+}
+
+func smudge(i int, rows []string) []string {
+	out := make([]string, len(rows))
+	copy(out, rows)
+	col := i % len(rows[0])
+	row := i / len(rows[0])
+	if col >= 0 && col < len(rows[0]) {
+		v := rows[row][col]
+		if v == '#' {
+			out[row] = out[row][:col] + "."  + out[row][col+1:]
+		} else {
+			out[row] = out[row][:col] + "#"  + out[row][col+1:]
+		}
+	}
+	return out
+}
+
+func findNewMirrorLoc(loc mirrorLoc, rows []string) (mirrorLoc, bool) {
+	if v, ok := findNewMirror(loc, "row", rows); ok {
+		return mirrorLoc{"row", v}, true
+	}
+	cols := swap(rows)
+	if v, ok := findNewMirror(loc, "col", cols); ok {
+		return mirrorLoc{"col", v}, true
+	}
+	return mirrorLoc{}, false
+}
+
+func findMirrorLoc(rows []string) (mirrorLoc, bool) {
+	if v, ok := findMirror(rows); ok {
+		return mirrorLoc{"row", v}, true
+	}
+	cols := swap(rows)
+	if v, ok := findMirror(cols); ok {
+		return mirrorLoc{"col", v}, true
+	}
+	return mirrorLoc{}, false
+}
+
+func swap(in []string) []string {
+	out := []string{}
+	for j:=0;j<len(in[0]);j++ {
+		o := ""
+		for i:=0;i<len(in);i++ {
+			o = o + string(in[i][j])
+		}
+		out = append(out, o)
+	}
+	return out
+}
+
+func findMirror(rows []string) (int, bool) {
+	for i:=0;i<len(rows)-1;i++ {
+		if rows[i] == rows[i+1] {
+			if isMirror(i, 0, rows) {
+				return i+1, true
+			}
+		}
+	}
+	return -1, false
+}
+
+func findNewMirror(loc mirrorLoc, orient string, rows []string) (int, bool) {
+	for i:=0;i<len(rows)-1;i++ {
+		if orient == loc.orient && i == loc.index - 1{ continue } 
+		if rows[i] == rows[i+1] {
+			if isMirror(i, 0, rows) {
+				return i+1, true
+			}
+		}
+	}
+	return -1, false
+}
+
+func isMirror(i int, offset int, rows []string) bool {
+	if i == 0 || i == len(rows) - 1 { return true }
+
+	if i - offset < 0 || i+1+offset > len(rows) - 1 { return true }
+
+	if rows[i+1+offset] == rows[i-offset] { 
+		return isMirror(i, offset+1, rows)
+	}
+	return false
+}