# Function to calculate permanent of a matrix
permanent <- function(mat) {
  n <- nrow(mat) # Number of rows in the matrix
  p <- 0 # Initialize permanent to 0
  permute <- function(col) { # Define a recursive function to calculate permanent
    if (length(col) == n) { # Base case
      p <<- p + prod(mat[cbind(1:n, col)]) # Update permanent
    } else { # Recursive case
      for (i in setdiff(1:n, col)) {
        permute(c(col, i)) # Recursively call permute with updated column
      }
    }
  }
  permute(integer(0)) # Call permute with an empty column to start the recursion
  return(p)
}
# Example usage
#mat <- matrix(c(1,2,3,4), nrow = 2)
#permanent(mat) 
# Returns 10