Error: subscript out of bounds (knight's tour) - r

Question

im new to R and im trying to solve for the minimum number of moves for a knight visit all the moves in a chess board.
I got the python code from:
https://www.geeksforgeeks.org/the-knights-tour-problem-backtracking-1/
and i tried to translate it to r.
But i am always getting the error and I don't know where I went wrong.
This is my code:
chess = rep(-1, times = 64)
board = matrix(data = chess, nrow = 8, ncol = 8, byrow = TRUE)
move_x = c(2, 1, -1, -2, -2, -1, 1, 2)
move_y = c(1, 2, 2, 1, -1, -2, -2, -1)
board[1, 1] = 0
pos = 1
valid_move <- function (x, y, board) {
if (x >= 1 & y >= 1 & x <= 8 & y <= 8 & board[x, y] == -1) {
return (T)
}
return (F)
}
solve <- function (board, curr_x, curr_y, move_x, move_y, pos) {
if (pos == 64) {
return (T)
}
for (i in seq(1:8)) {
new_x = curr_x + move_x[i]
new_y = curr_y + move_y[i]
if (valid_move(new_x, new_y, board)) {
board[new_x, new_y] = pos
if (solve(board, new_x, new_y, move_x, move_y, pos+1)) {
return (TRUE)
}
board[new_x, new_y] = -1
}
}
}
main <- function() {
sims = 10
ctr = 0
number_of_moves = c()
solve(board, 1, 1, move_x, move_y, pos)
print(paste("Minimum number of moves: ", pos))
}
main()
Thanks!

Answer 1

The problem is that the python code relies on short-circuiting to prevent out-of-bounds errors. & will not short-circuit so you need to use &&.
Here is an example
FALSE && stop()
#> [1] FALSE
FALSE & stop()
#> Error:
Update valid_move to this
valid_move <- function (x, y, board) {
# Changed to && to allow short-circuiting
# if (x >= 1 & y >= 1 & x <= 8 & y <= 8 & board[x, y] == -1) {
if (x >= 1 && y >= 1 && x <= 8 && y <= 8 && board[x, y] == -1) {
return (T)
}
return (F)
}