Tiny System design

TinyURL

535. Encode and Decode TinyURL

alphabet = string.ascii_letters + '0123456789'
class Codec:
    
    def __init__(self):
        self.long_short = {}
        self.short_long = {}
    def encode(self, longUrl):
        while longUrl not in self.long_short:
            while True:
                short = ''.join(random.choice(alphabet) for _ in range(6))
                if short not in self.short_long:break        
            self.short_long[short] = longUrl
            self.long_short[longUrl] = short
        return 'http://' + short
    def decode(self, shortUrl):
        if shortUrl[-6:] not in self.short_long:return ""
        return self.short_long[shortUrl[-6:]]
# Your Codec object will be instantiated and called as such:
# codec = Codec()
# codec.decode(codec.encode(url))

Design a snake game

353. Design Snake Game

class SnakeGame:
def __init__(self, width: int, height: int, food: List[List[int]]):
        """
        Initialize your data structure here.
        @param width - screen width
        @param height - screen height 
        @param food - A list of food positions
        E.g food = [[1,1], [1,0]] means the first food is positioned at [1,1], the second is at [1,0].
        """
        self.R = height
        self.C = width
        self.food = food[::-1]
        self.dire = {'U':(-1,0),'D':(1,0),'L':(0,-1),'R':(0,1)}
        self.snake = collections.deque([(0,0)])
def move(self, direction: str) -> int:
        """
        Moves the snake.
        @param direction - 'U' = Up, 'L' = Left, 'R' = Right, 'D' = Down 
        @return The game's score after the move. Return -1 if game over. 
        Game over when snake crosses the screen boundary or bites its body.
        """
        di, dj = self.dire[direction]
        i, j = self.snake[-1]
        r, c = i+di, j+dj
        if r<0 or r>=self.R or c<0 or c>=self.C:return -1
        elif self.food and [r,c]==self.food[-1]:
            self.food.pop()
            self.snake.append((r,c))
            return len(self.snake)-1
        elif (r,c) !=self.snake[0] and (r,c) in self.snake:
            return -1
        else:
            self.snake.popleft()
            self.snake.append((r,c))
            return len(self.snake)-1
# Your SnakeGame object will be instantiated and called as such:
# obj = SnakeGame(width, height, food)
# param_1 = obj.move(direction)

Programing tips

collections.deque can not slice however, it can be visited by index

>>> import collections
>>> a = collections.deque([1,2,3,4])
>>> a[1:]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: sequence index must be integer, not 'slice'
>>> a[0]
1
>>> a[-1]
4
>>>