std :: map< int，int>与矢量矢量 [英] std::map<int, int> vs. vector of vector

问题描述

我需要一个容器来根据两个属性source（int）和destination（int）存储一个值（int），即当一个源发送到目的地时，我需要将它作为元素存储在容器中。源由唯一的int ID（0-M的整数）标识，其中M是几十到几百，目的地（0-N）也是如此。

我一直在使用向量（vector（int））这意味着按照源（目的地（值））的顺序。后续进程需要检查此容器，以查看特定源和特定目标是否存在元素 - 它将需要区分空空格和已填充的空格。容器有非常稀疏的可能性。

要存储的值可以是0，所以我没有成功试图找出空间是否为空，因为我似乎不能做像container [M] [N] .empty（）。

我没有地图使用经验，但我看到了另一个 post 表明一个映射可能是有用的，并且 std :: map 类似于向量<向量< int>> 。

总结：

1. 有一种方法可以检查向量'space'的特定向量是否为空（因为我无法将其与0比较）


2. 是 std :: map 更好的用途，我如何使用？






解决方案

我需要一个容器根据两个属性存储一个值b source（int）and destination（int）





  std :: map< std :: pair< int，int>，int> 
  





后续进程需要检查此容器， b $ b元素存在于特定源中，特定的
目标 - 它将需要区分空的'空间'
和填充的空间。

< blockquote>

  std :: map :: find 
  

http://www.cplusplus.com/reference/ map / map / find /

容器可能非常稀疏。

使用std :: map。容器的正确选择是基于你需要找到的东西，以及你需要插入/删除的东西。如果你想快速找到东西，使用地图。

I need a container to store a value (int) according to two attributes, source (int) and destination (int) i.e. when a source sends something to a destination, I need to store it as an element in a container. The source is identified by a unique int ID (an integer from 0-M), where M is in the tens to hundreds, and so is the destination (0-N). The container will be updated by iterations of another function.

I have been using a vector(vector(int)) which means goes in the order of source(destination(value)). A subsequent process needs to check this container, to see if an element exists in for a particular source, and a particular destination - it will need to differentiate between an empty 'space' and a filled one. The container has the possibility of being very sparse.

The value to be stored CAN be 0 so I haven't had success trying to find out if the space is empty, since I can't seem to do something like container[M][N].empty().

I have no experience with maps, but I have seen another post that suggests a map might be useful, and an std::map<int, int> seems to be similar to a vector<vector<int>>.

To summarise:

1. Is there a way to check if a specific vector of vector 'space' is empty (since I can't compare it to 0)
2. Is a std::map<int, int> better for this purpose, and how do I use one?

解决方案

I need a container to store a value (int) according to two attributes, source (int) and destination (int)

std::map<std::pair<int, int>, int>

A subsequent process needs to check this container, to see if an element exists in for a particular source, and a particular destination - it will need to differentiate between an empty 'space' and a filled one.

std::map::find

http://www.cplusplus.com/reference/map/map/find/

The container has the possibility of being very sparse.

Use a std::map. The "correct" choice of a container is based on how you need to find things and how you need to insert/delete things. If you want to find things fast, use a map.

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