SIZE = 5
plateau = [True,]*(SIZE**2)

print "Plateau:"
for i in xrange(0,SIZE**2,SIZE):
    print ','.join(map(lambda d: "%2d" %d, range(SIZE**2)[i:i+SIZE]))
print

def test(f):
    print ["%2d=%s" %(f(i),plateau[f(i)]) for i in xrange(SIZE)], 
    print '=', 
    print sum([plateau[f(i)] is True for i in xrange(SIZE)])==SIZE    

WALK_FCT = {"diag_1":lambda i:i+i*SIZE,
            "diag_2":lambda i: (SIZE)*(SIZE-(i+1))+(i+1)-1,
            "hor_N":lambda n: lambda i: n*SIZE+i,
            "ver_N":lambda n: lambda i: i*SIZE+n}

ALL_TESTS = [WALK_FCT["diag_1"], WALK_FCT["diag_2"]]
ALL_TESTS.extend(WALK_FCT["hor_N"](n) for n in xrange(SIZE))
ALL_TESTS.extend(WALK_FCT["ver_N"](n) for n in xrange(SIZE))

for f in ALL_TESTS:
    test(f)