iterator用法

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#include <iostream>
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#include <vector>
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#include <list>
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int main() {
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    // 1. 使用 vector (随机访问迭代器)
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    std::vector<int> vec = {1, 2, 3, 4, 5};
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    std::cout << "Vector iteration: ";
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    // 使用 begin() 和 end() 获取迭代器
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    for (std::vector<int>::iterator it = vec.begin(); it != vec.end(); ++it) {
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        std::cout << *it << " "; // 通过 * 解引用访问元素
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    }
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    std::cout << std::endl;
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    // 2. 使用 list (双向迭代器)
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    std::list<std::string> lst = {"Hello", "World", "C++"};
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    std::cout << "List iteration: ";
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    // 使用 auto 简化迭代器类型声明
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    for (auto it = lst.begin(); it != lst.end(); ++it) {
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        std::cout << *it << " ";
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    }
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    std::cout << std::endl;
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    // 3. 反向迭代
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    std::cout << "Reverse iteration: ";
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    for (auto it = vec.rbegin(); it != vec.rend(); ++it) { // rbegin(), rend() 返回反向迭代器
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        std::cout << *it << " ";
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    }
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    std::cout << std::endl;
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    // 4. 基于范围的 for 循环 (底层也是使用迭代器)
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    std::cout << "Range-based for loop: ";
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    for (const auto& value : vec) {
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        std::cout << value << " ";
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    }
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    std::cout << std::endl;
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    return 0;
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}

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# 1. 使用内置可迭代对象 (list, tuple, string, dict)
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my_list = [1, 2, 3, 4, 5]
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print("List iteration: ", end="")
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for item in my_list:
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    print(item, end=" ")
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print()
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# 2. 手动模拟 for 循环的过程
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print("Manual iteration: ", end="")
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iterator_obj = iter(my_list) # 获取迭代器
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while True:
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    try:
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        item = next(iterator_obj)
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        print(item, end=" ")
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    except StopIteration:
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        break
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print()
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# 3. 字典迭代
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my_dict = {'a': 1, 'b': 2, 'c': 3}
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print("Dict iteration (keys): ", end="")
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for key in my_dict:
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    print(key, end=" ")
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print()
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print("Dict iteration (items): ", end="")
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for key, value in my_dict.items():
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    print(f"{key}:{value}", end=" ")
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print()
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# 4. 创建一个自定义迭代器
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class CountDown:
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    def __init__(self, start):
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        self.current = start
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    def __iter__(self):
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        return self
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    def __next__(self):
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        if self.current <= 0:
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            raise StopIteration
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        else:
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            num = self.current
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            self.current -= 1
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            return num
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print("Custom iterator: ", end="")
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counter = CountDown(3)
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for num in counter:
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    print(num, end=" ")