二维 unordered_map [英] Two dimensional unordered_map

问题描述

typedef boost::unordered_map<int, void*> OneDimentionalNodes;
typedef boost::unordered_map<int, OneDimentionalNodes> TwoDimentionalNodes;

TwoDimentionalNodes nodes;

这有效吗?

我不使用任何散列函数，因为 unordered_maps 的键是单个整数.它可以编译，但是当我像这样迭代它时，它在尝试访问 this->hash_function()(k); 时崩溃了；

i don't use any hash functions since keys of the unordered_maps' are single integers. it compiles, but when i iterate it like this, it crashes while trying to access this->hash_function()(k);

for (TwoDimentionalNodes::iterator it= nodes.begin(); it != nodes.end() ; ++it)
{
   for(OneDimentionalNodes::iterator it2 = nodes[it->first].begin(); it2 != nodes[it->first].end() ; ++it2)
    {
   // do stuff
    }
}

我也对其他容器开放

• O(1) 访问
• O(n) 迭代
• 稀疏

推荐答案

如果你只需要遍历所有元素，而不需要遍历特定维度，那么你可以使用一个简单的pair作为你的keyunordered_map，像这样:

If you just need to iterator over all elements, and it is not required to loop over a specific dimension, then you could use a simple pair as key for your unordered_map, like this:

typedef std::pair<int,int> Coordinates;
typedef std::unordered_map<Coordinates,void *> TwoDimensionalNodes;

(注意我使用了 STL 而不是 Boost，unordered_map 现在也是标准 STL 的一部分).

(notice I used STL instead of Boost, unordered_map is now also part of the standard STL).

获取一个特定的值很简单:

Getting a specific value is simply writing:

twoDimensionalNodes[std::make_pair(x,y)]

(或者，如果您不确定该值是否在您的地图中，请使用 find).

(or use find if you're not sure if that value is in your map).

要迭代，只需迭代无序映射:

To iterate, just iterate over the unordered map:

for (auto it=twoDimensionalNodes.begin();it!=twoDimensionalNodes.end();++it)
   {
   std::cout << "x=" << it->first.first;
   std::cout << "y=" << it->first.second;
   std::cout << "value=" << it->second;
   }

为了让它更具可读性，我更喜欢先从迭代器中获取坐标，如下所示:

To make it a bit more readable, I prefer getting the coordinates first from the iterator, like this:

for (auto it=twoDimensionalNodes.begin();it!=twoDimensionalNodes.end();++it)
   {
   Coordinates &coordinates = it->first;
   std::cout << "x=" << coordinates.first;
   std::cout << "y=" << coordinates.second;
   std::cout << "value=" << it->second;
   }

如果您有超过 2 个维度，请使用 std::tuple，或者只需编写您自己的 Coordinates 类以用作地图的键.

If you have more than 2 dimensions, use std::tuple, or simply write your own Coordinates class to be used as key for the map.

这篇关于二维 unordered_map的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！