Snail

import math
def tosnail(ans):
  if(ans==[]):
    return [[]]
  n=int(math.sqrt(len(ans)))
  arr=[[0 for i in range(n)] for j in range(n)]
  for i in range(n):
    for j in range(i,n-i):#left
      arr[i][j]=ans.pop()
    for j in range(i+1,n-i):#down
      arr[j][n-i-1]=ans.pop()
    for j in range(n-i-2,i-1,-1):#right
      arr[n-i-1][j]=ans.pop()
    for j in range(n-i-2,i,-1):#up
      arr[j][i]=ans.pop()
  return arr

def snail(arr):
  if(arr==[[]]):
    return []
  n=len(arr)
  ans=[]
  for i in range(math.ceil(n/2)):
    for j in range(i,n-i):#left
      ans.append(arr[i][j])
    for j in range(i+1,n-i):#down
      ans.append(arr[j][n-i-1])
    for j in range(n-i-2,i-1,-1):#right
      ans.append(arr[n-i-1][j])
    for j in range(n-i-2,i,-1):#up
      ans.append(arr[j][i])
  return tosnail(ans)

arr = [[1,2,3,4,5],
       [6,7,8,9,10],
       [11,12,13,14,15],
       [16,17,18,19,20],
       [21,22,23,24,25]
]
snail(arr)