当元素大小超过数组大小的1/2时调整数组大小

class DynamicArray:
    def __init__(self):
        self.array = [None] * 1  # 初始大小为1
        self.length = 0  # 当前元素数量
        self.capacity = 1  # 数组容量

    def append(self, item):
        if self.length == self.capacity:
            self._resize(2 * self.capacity)  # 扩容为当前容量的两倍
        self.array[self.length] = item
        self.length += 1

    def _resize(self, new_capacity):
        new_array = [None] * new_capacity
        for i in range(self.length):
            new_array[i] = self.array[i]
        self.array = new_array
        self.capacity = new_capacity

# 使用示例
dynamic_array = DynamicArray()
dynamic_array.append(1)
dynamic_array.append(2)
dynamic_array.append(3)
print(dynamic_array.array)  # 输出: [1, 2, 3, None]