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Solution 8: Serpentine Dynamics (Snake Game Design)

Approach Explanation

We use a deque (double-ended queue) to store the body coordinates of the snake. The front of the deque is the head. We also use a hash set to store the body parts for O(1) crash detection.

Step-by-Step Logic

  1. __init__: Store width, height, food list, and initialize snake = deque([(0,0)]), body = set([(0,0)]), food_idx = 0.
  2. move(direction):
    • Calculate new head position berdasarkan direction.
    • Check wall collision. If yes, return -1.
    • Check if new head is at food[food_idx].
      • If yes, increment food_idx and score. Don't pop tail.
      • If no, pop tail from snake and body.
    • Check body collision (is new head in body?). If yes, return -1.
    • Add new head to snake and body.
    • Return score.

Complexity

  • Time Complexity: O(1) per move.
  • Space Complexity: O(N + L), where N is snake length and L is food count.

Code

from collections import deque

class SnakeGame:
    def __init__(self, width: int, height: int, food: list[list[int]]):
        self.w, self.h = width, height
        self.food = food
        self.food_idx = 0
        self.snake = deque([(0, 0)])
        self.body = {(0, 0)}
        self.dir_map = {'U': (-1, 0), 'D': (1, 0), 'L': (0, -1), 'R': (0, 1)}

    def move(self, direction: str) -> int:
        r, c = self.snake[0]
        dr, dc = self.dir_map[direction]
        nr, nc = r + dr, c + dc
        
        # 1. Wall collision
        if not (0 <= nr < self.h and 0 <= nc < self.w):
            return -1
            
        # 2. Food check
        has_food = (self.food_idx < len(self.food) and 
                    [nr, nc] == self.food[self.food_idx])
        
        if not has_food:
            tail = self.snake.pop()
            self.body.remove(tail)
            
        # 3. Body collision
        if (nr, nc) in self.body:
            return -1
            
        self.snake.appendleft((nr, nc))
        self.body.add((nr, nc))
        
        if has_food:
            self.food_idx += 1
            
        return len(self.snake) - 1