项目说明：https://inst.eecs.berkeley.edu/~cs61a/sp21/proj/ants/
蚂蚁大战蜜蜂 灵感来源：植物大战僵尸（Plants Vs. Zombies，PVZ）
样图：

• 游戏说明
• Phase 1: Basic gameplay
  • Problem 1 (1 pt)
  • Problem 2 (2 pt)
  • Problem 3 (2 pt)

游戏说明

游戏按轮次进行，每一轮中，新的蜜蜂都可能进入蚁群领地。然后，放置新的蚂蚁来保卫它们的领地。 最后，所有昆虫（蚂蚁，蜜蜂）都会采取单独的行动。蜜蜂沿着tunnel从右往左移动，遇到蚂蚁则攻击蚂蚁。不同类型的蚂蚁执行不同的动作，例如收集更多食物或向蜜蜂扔树叶。 当一只蜜蜂到达tunnel尽头或者摧毁了 QueenAnt（如果存在），你就输了；整个蜜蜂舰队都被打败，你就赢了；游戏结束。
核心概念和核心类都跟PVZ类似。

Phase 1: Basic gameplay

Problem 1 (1 pt)

Part A: 当前放置任一类型Ant都没有cost，基类Ant的food_cost为0。任务：根据表格的"Food cost"重写HarvesterAnt和ThrowerAnt的类属性。

Part B: 放置ant需要消耗食物，HarvesterAnt生产食物（类似PVZ向日葵） 任务：完成HarvesterAnt action方法。
代码：

class HarvesterAnt(Ant):
    """HarvesterAnt produces 1 additional food per turn for the colony."""

    name = 'Harvester'
    implemented = True
    # OVERRIDE CLASS ATTRIBUTES HERE
    food_cost = 2

    def action(self, gamestate):
        """Produce 1 additional food for the colony.

        gamestate -- The GameState, used to access game state information.
        """
        # BEGIN Problem 1
        "*** YOUR CODE HERE ***"
        gamestate.food += 1
        # END Problem 1

class ThrowerAnt(Ant):
    """ThrowerAnt throws a leaf each turn at the nearest Bee in its range."""

    name = 'Thrower'
    implemented = True
    damage = 1
    # ADD/OVERRIDE CLASS ATTRIBUTES HERE
    food_cost = 3

Problem 2 (2 pt)

任务：完成 Place.__init__记录入口entrance。
分析：类似链表结构，创建Place对象时，entrance为None；如果这个对象的exit不为None，将这个exit的entrance设置为这个对象。
代码：

class Place:
    """A Place holds insects and has an exit to another Place."""

    def __init__(self, name, exit=None):
        """Create a Place with the given NAME and EXIT.

        name -- A string; the name of this Place.
        exit -- The Place reached by exiting this Place (may be None).
        """
        self.name = name
        self.exit = exit
        self.bees = []        # A list of Bees
        self.ant = None       # An Ant
        self.entrance = None  # A Place
        # Phase 1: Add an entrance to the exit
        # BEGIN Problem 2
        "*** YOUR CODE HERE ***"
        if self.exit:
            self.exit.entrance = self
        # END Problem 2

Problem 3 (2 pt)

ThrowerAnt类似豌豆射手，需要根据nearest_bee方法确定攻击哪只蜜蜂(攻击身前且不在蜂巢中的蜜蜂)。
任务：修改nearest_bee让它返回最近的蜜蜂之一。

• 从豌豆射手ThrowerAnt的位置开始
• 对于每个place，如果其中有蜜蜂，则随机返回蜜蜂之一；如果没有蜜蜂，查找更前面的place
• 如果没有蜜蜂可以攻击，返回None

遍历豌豆射手身前的place时，由于self.place不会变，所以引入新参数next_place，place中没有蜜蜂，则赋值为下一个格子next_place.entrance，直到找到有蜜蜂的place或者到达蜂巢。
注意：phase 2中problem 4有新要求，要考虑ant的攻击距离，相应的problem 3部分会在phase 2进行修改。

class ThrowerAnt(Ant):
    """ThrowerAnt throws a leaf each turn at the nearest Bee in its range."""

    name = 'Thrower'
    implemented = True
    damage = 1
    # ADD/OVERRIDE CLASS ATTRIBUTES HERE
    food_cost = 3

    def nearest_bee(self, beehive):
        """Return the nearest Bee in a Place that is not the HIVE (beehive), connected to
        the ThrowerAnt's Place by following entrances.

        This method returns None if there is no such Bee (or none in range).
        """
        # BEGIN Problem 3 and 4
        # 不能改变ant的位置self.place
        next_place = self.place
        while not next_place.is_hive():
            if next_place.bees:
                return bee_selector(next_place.bees)  # REPLACE THIS LINE
            next_place = next_place.entrance
        return None
        # END Problem 3 and 4