在地图中查找最小值 [英] Finding minimum value in a Map

问题描述

我有一张地图，我想在地图中找到最小值（右侧）。现在这里是我怎么做了

I have a map and I want to find the minimum value (right hand side) in the map. Right now here is how I did it

bool compare(std::pair<std::string ,int> i, pair<std::string, int> j) {
  return i.second < j.second;
}
////////////////////////////////////////////////////
std::map<std::string, int> mymap;

mymap["key1"] = 50;
mymap["key2"] = 20;
mymap["key3"] = 100;

std::pair<char, int> min = *min_element(mymap.begin(), mymap.end(), compare); 
std::cout << "min " << min.second<< " " << std::endl;

这很好，我可以得到最小值的问题是，在我的类中似乎不工作

This works fine and I'm able to get the minimum value the problem is when I put this code inside my class it doesn't seem to work

int MyClass::getMin(std::map<std::string, int> mymap) {
  std::pair<std::string, int> min = *min_element(mymap.begin(), mymap.end(), 
                                                 (*this).compare);
                                                 //error probably due to this

  return min.second; 
}

bool MyClass::compare(
    std::pair<std::string, int> i, std::pair<std::string, int> j) { 
  return i.second < j.second; 
}

还有一个更好的解决方案，不涉及写入额外的比较函数

Also is there a better solution not involving to writing the additional compare function

推荐答案

最好的方法是使用函子，这是保证最快的调用：

You have a few options. The "best" way to do this is with a functor, this is guaranteed to be the fastest to call:

typedef std::pair<std::string, int> MyPairType;
struct CompareSecond
{
    bool operator()(const MyPairType& left, const MyPairType& right) const
    {
        return left.second < right.second;
    }
};



int MyClass::getMin(std::map<std::string, int> mymap) 
{
  std::pair<std::string, int> min 
      = *min_element(mymap.begin(), mymap.end(), CompareSecond());
  return min.second; 
}

（您也可以嵌套 CompareSecond class in MyClass 。

(You can also nest the CompareSecond class inside MyClass.

使用现在的代码，您可以轻松地修改它，但是，只需使函数 static 并使用正确的语法：

With the code you have now, you can easily modify it to work, however. Just make the function static and use the correct syntax:

static bool 
MyClass::compare(std::pair<std::string, int> i, std::pair<std::string, int> j) 
{ 
  return i.second < j.second; 
}

int MyClass::getMin(std::map<std::string, int> mymap) 
{
  std::pair<std::string, int> min = *min_element(mymap.begin(), mymap.end(), 
                                                 &MyClass::compare);
  return min.second; 
}

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