alternative solution to exercise 87

Added a more elegant (but more cryptic) solution with reshape and
swapaxes.

Removed one of the existing alternative solutions because it was a
duplicate of a previous alternative solution.

source/exercises100.ktx

@@ -1333,11 +1333,8 @@ k = 4
 windows = np.lib.stride_tricks.sliding_window_view(Z, (k, k))
 S = windows[::k, ::k, ...].sum(axis=(-2, -1))
 
-# Author: Jeff Luo (@Jeff1999)
-
-Z = np.ones((16, 16))
-k = 4
-print(sliding_window_view(Z, window_shape=(k, k))[::k, ::k].sum(axis=(-2, -1)))
+# alternative solution (by @Gattocrucco)
+S = Z.reshape(4, 4, 4, 4).swapaxes(1, 2).sum((2, 3))
 
 < q88
 How to implement the Game of Life using numpy arrays? (★★★)