Source code in the r programming language

spiral <- function(n) matrix(order(cumsum(rep(rep_len(c(1, n, -1, -n), 2 * n - 1), n - seq(2 * n - 1) %/% 2))), n, byrow = T) - 1

spiral(5)

spiral_matrix <- function(n) {
    spiralv <- function(v) {
        n <- sqrt(length(v))
        if (n != floor(n))
            stop("length of v should be a square of an integer")
        if (n == 0)
            stop("v should be of positive length")
        if (n == 1)
            m <- matrix(v, 1, 1)
        else
            m <- rbind(v[1:n], cbind(spiralv(v[(2 * n):(n^2)])[(n - 1):1, (n - 1):1], v[(n + 1):(2 * n - 1)]))
        m
    }
    spiralv(1:(n^2))
}

spiralMatrix <- function(n)
{
  spiral <- matrix(0, nrow = n, ncol = n)
  firstNumToWrite <- 0
  neededLength <- n
  startPt <- cbind(1, 0)#(1, 0) is needed for the first call to writeRight to work. We need to start in row 1.
  writingDirectionIndex <- 0
  #These two functions select a collection of adjacent elements and replaces them with the needed sequence.
  #This heavily uses R's vector recycling rules.
  writeDown <- function(seq) spiral[startPt[1] + seq, startPt[2]] <<- seq_len(neededLength) - 1 + firstNumToWrite
  writeRight <- function(seq) spiral[startPt[1], startPt[2] + seq] <<- seq_len(neededLength) - 1 + firstNumToWrite
  while(firstNumToWrite != n^2)
  {
    writingDirectionIndex <- writingDirectionIndex %% 4 + 1
    seq <- seq_len(neededLength)
    switch(writingDirectionIndex,
           writeRight(seq),
           writeDown(seq),
           writeRight(-seq),
           writeDown(-seq))
    if(writingDirectionIndex %% 2) neededLength <- neededLength - 1
    max <- max(spiral)
    firstNumToWrite <- max + 1
    startPt <- which(max == spiral, arr.ind = TRUE)
  }
  spiral
}