https://www.codewars.com/kata/5671d975d81d6c1c87000022/train/python

4_By_4_Skyscrapers_codewars.py

# No two skyscrapers in a row or column may have the same number of floors
# The height of the skyscrapers is between 1 and 4
# so conservative upper bound is (4!)**4 = 331776
# A clue is the number of skyscrapers you can see.
import itertools
n=4
def solve_puzzle (clues):
    grid=[]
    
    def validate_column(clue, c, from_top):
        can_see, last_seen_height = 0, -1
        for i in (range(0, n) if from_top else range(n-1, -1,-1)):
            if grid[i][c] > last_seen_height:
                can_see, last_seen_height = can_see+1, grid[i][c]
        return can_see == clue
    
    def validate_row(clue, r, from_left):
        can_see, last_seen_height = 0, -1
        for i in (range(0, n) if from_left else range(n-1, -1,-1)):
            if grid[r][i] > last_seen_height:
                can_see, last_seen_height = can_see+1, grid[r][i]
        return can_see == clue

#     grid = ( (2,1,4,3),
#             (3,4,1,2),
#             (4,2,3,1),
#             (1,3,2,4))
#         the test case
#     print( validate_column(1,2,True), validate_column(2,3,True), validate_row(2,1,False), validate_column(3,2,False), validate_row(1,2,True),  )
        
    def validate_grid():
        for i, v in enumerate(clues):
            if v == 0: continue
            if i // n == 0 and not validate_column(v, i, True): # column down
                return False
            elif i // n == 1 and not validate_row(v, i % n, False): # row right
                return False
            elif i // n == 2 and not validate_column(v, n - (i % n) - 1, False): # column up
                return False
            elif i // n == 3 and not validate_row(v, n - (i % n) - 1, True): # row left
                return False
        return True
    
#     print(validate_grid())

    res = None
    def rec(a=0,b=0,c=0,d=0):
        nonlocal res
        if res: return
        if all(map(lambda x: x == (1<<n)-1 << 1, (a,b,c,d) )):
            # if all bitmasks are 01111
            if validate_grid():
                res = tuple(tuple(l) for l in grid)
            return
        for perm in map(lambda x: list(map(lambda y: y+1, x)), itertools.permutations(range(n))):
            if res: return
            used = [a,b,c,d]
            ok = True
            for i in range(n):
                if used[i] & (1<<perm[i]):
                    ok = False
                    break
                else: used[i] |= (1<<perm[i])
            if ok:
                grid.append(perm)
                rec(*used)
                grid.pop()
    rec()
    return res