插入到前面的矢量 [英] Inserting into a vector at the front

问题描述

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

是 std :: Vector class。

此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，给定这种返回类型，什么是最有效的方式（这是一个更大的程序的一部分，我运行速度是至关重要的，所以我寻找最计算高效的方式）。是以下吗？

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

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

基本上，在代码2中，是参数

Essentially, in Code 2, is the parameter,

intvector.begin() 

Costly在计算方面进行评估，与在代码1中使用返回的迭代器相比，或者应该同样便宜/昂贵吗？

"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

p>获得插入点的效率至少是没有问题的 - 每次插入时，不断地改变现有数据的效率就会很低。

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，这是它的设计目的。

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

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