在前面插入向量 [英] Inserting into a vector at the front

问题描述

iterator insert ( iterator position, const T& x );

是std::Vector类的插入操作符的函数声明.

Is the function declaration of the insert operator of the std::Vector class.

这个函数的返回类型是一个指向插入元素的迭代器.我的问题是，鉴于这种返回类型，最有效的方法是什么(这是我正在运行的更大程序的一部分，速度至关重要，所以我正在寻找最计算效率的方法) 在开头插入.是下面的吗?

This function's return type is an iterator pointing to the inserted element. My question is, given this return type, what is the most efficient way (this is part of a larger program I am running where speed is of the essence, so I am looking for the most computationally efficient way) of inserting at the beginning. Is it the following?

//Code 1
vector<int> intvector;
vector<int>::iterator it;
it = myvector.begin();
for(int i = 1; i <= 100000; i++){
    it = intvector.insert(it,i);
}

或者，

//Code 2
vector<int> intvector;
for(int i = 1; i <= 100000; i++){
    intvector.insert(intvector.begin(),i);
}

本质上，在代码 2 中，是参数，

Essentially, in Code 2, is the parameter,

intvector.begin() 

与在代码 1 中使用返回的迭代器相比，成本高"在计算上进行评估，或者两者都应该同样便宜/成本高?

"Costly" to evaluate computationally as compared to using the returned iterator in Code 1 or should both be equally cheap/costly?

推荐答案

获取插入点的效率一点也不重要 - 每次执行时不断地将现有数据洗牌的低效率会让它相形见绌插入.

The efficiency of obtaining the insertion point won't matter in the least - it will be dwarfed by the inefficiency of constantly shuffling the existing data up every time you do an insertion.

为此使用 std::deque，这就是它的设计目的.

Use std::deque for this, that's what it was designed for.

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