For problem statement at 2000-2999/2000-2099/2040-2049/2045/problemM.txt this is a correct solution, but verifier at 2000-2999/2000-2099/2040-2049/2045/verifierM.go ends with panic: runtime error: index out of range [3] with length 3

goroutine 1 [running]:
main.simulate({{0xfcb97, 0x7}, 0x4, 0x4, {0x40000b4100, 0x4, 0x4}}, 0xffffffffffffffff, 0x3, 0x2, ...)
	/home/ubuntu/codeforces/2000-2999/2000-2099/2040-2049/2045/verifierM.go:257 +0x2d8
main.evaluate({{0xfcb97, 0x7}, 0x4, 0x4, {0x40000b4100, 0x4, 0x4}})
	/home/ubuntu/codeforces/2000-2999/2000-2099/2040-2049/2045/verifierM.go:174 +0xb0
main.main()
	/home/ubuntu/codeforces/2000-2999/2000-2099/2040-2049/2045/verifierM.go:56 +0x34c
exit status 2 can you fix the verifier? package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func main() {
	in := bufio.NewReaderSize(os.Stdin, 1<<20)
	out := bufio.NewWriterSize(os.Stdout, 1<<20)
	defer out.Flush()

	var R, C int
	fmt.Fscan(in, &R, &C)

	rowLists := make([][]int, R)
	colLists := make([][]int, C)
	types := make([]byte, 0)

	for r := 0; r < R; r++ {
		var s string
		fmt.Fscan(in, &s)
		for c := 0; c < C; c++ {
			if s[c] != '.' {
				id := len(types)
				types = append(types, s[c])
				rowLists[r] = append(rowLists[r], id)
				colLists[c] = append(colLists[c], id)
			}
		}
	}

	M := len(types)

	left := make([]int, M)
	right := make([]int, M)
	up := make([]int, M)
	down := make([]int, M)
	for i := 0; i < M; i++ {
		left[i], right[i], up[i], down[i] = -1, -1, -1, -1
	}

	for r := 0; r < R; r++ {
		arr := rowLists[r]
		for i, id := range arr {
			if i > 0 {
				left[id] = arr[i-1]
			}
			if i+1 < len(arr) {
				right[id] = arr[i+1]
			}
		}
	}

	for c := 0; c < C; c++ {
		arr := colLists[c]
		for i, id := range arr {
			if i > 0 {
				up[id] = arr[i-1]
			}
			if i+1 < len(arr) {
				down[id] = arr[i+1]
			}
		}
	}

	const (
		N = 0
		E = 1
		S = 2
		W = 3
	)

	reflSlash := [4]int{W, S, E, N}
	reflBack := [4]int{E, N, W, S}
	opp := [4]int{S, W, N, E}

	nextState := make([]int, M*4)
	for m := 0; m < M; m++ {
		for inSide := 0; inSide < 4; inSide++ {
			var outSide int
			if types[m] == '/' {
				outSide = reflSlash[inSide]
			} else {
				outSide = reflBack[inSide]
			}
			nm := -1
			switch outSide {
			case N:
				nm = up[m]
			case E:
				nm = right[m]
			case S:
				nm = down[m]
			case W:
				nm = left[m]
			}
			if nm == -1 {
				nextState[m*4+inSide] = -1
			} else {
				nextState[m*4+inSide] = nm*4 + opp[outSide]
			}
		}
	}

	entries := make([]string, 0, 2*(R+C))
	starts := make([]int, 0, 2*(R+C))

	for c := 0; c < C; c++ {
		entries = append(entries, "N"+strconv.Itoa(c+1))
		if len(colLists[c]) == 0 {
			starts = append(starts, -1)
		} else {
			starts = append(starts, colLists[c][0]*4+N)
		}
	}
	for c := 0; c < C; c++ {
		entries = append(entries, "S"+strconv.Itoa(c+1))
		if len(colLists[c]) == 0 {
			starts = append(starts, -1)
		} else {
			arr := colLists[c]
			starts = append(starts, arr[len(arr)-1]*4+S)
		}
	}
	for r := 0; r < R; r++ {
		entries = append(entries, "E"+strconv.Itoa(r+1))
		if len(rowLists[r]) == 0 {
			starts = append(starts, -1)
		} else {
			arr := rowLists[r]
			starts = append(starts, arr[len(arr)-1]*4+E)
		}
	}
	for r := 0; r < R; r++ {
		entries = append(entries, "W"+strconv.Itoa(r+1))
		if len(rowLists[r]) == 0 {
			starts = append(starts, -1)
		} else {
			starts = append(starts, rowLists[r][0]*4+W)
		}
	}

	stateSeen := make([]int, M*4)
	mirrorSeen := make([]int, M)
	ans := make([]string, 0)

	for i, start := range starts {
		if start == -1 {
			continue
		}
		sim := i + 1
		count := 0
		s := start
		for s != -1 && stateSeen[s] != sim {
			stateSeen[s] = sim
			m := s >> 2
			if mirrorSeen[m] != sim {
				mirrorSeen[m] = sim
				count++
			}
			s = nextState[s]
		}
		if count == M {
			ans = append(ans, entries[i])
		}
	}

	fmt.Fprintln(out, len(ans))
	if len(ans) > 0 {
		for i, s := range ans {
			if i > 0 {
				fmt.Fprint(out, " ")
			}
			fmt.Fprint(out, s)
		}
		fmt.Fprintln(out)
	}
}