如何从实体向量中找到最小值？

Question

class enemy{
    ....
}

std::vector<std::unique_ptr<enemy> > enemies1;

for (unsigned i = 0; i < 3; ++i)
    enemies1.emplace_back(...);

for (int i = 0; i < enemies1.size(); i++) {
    std::cout << i <<"x: " << enemies1[i]->rect.getPosition().x << std::endl;
}

output:

100
200
400

How could I get the minimum coordinate value from multiple enemies in the vector? I want to detect the nearest enemy from the player, eg the player's coordinate is 50 and enemies are at 100, 200, 400, as you see in the above example. I want to detect the nearest enemy in the vector.

Answer 1

You can use min_element from

#include <algorithm>
#include <iostream>
#include <vector>

struct enemy_t
{
    explicit enemy_t(const double d) :
        distance{ d }
    {
    }

    double distance;
};

int main()
{
    // create a vector of enemies using the constructor with one double
    std::vector<enemy_t> enemies{ 100.0,400.0,200.0,10.0 };

    // the last argument to min_element is a lambda function 
    // it helps you define by what condition you want to find your element.
    auto enemy = std::min_element(enemies.begin(), enemies.end(), [](const enemy_t& lhs, const enemy_t& rhs)
    {
        return lhs.distance < rhs.distance;
    });

    std::cout << "The minimum distance found = " << enemy->distance << "\n";

    return 0;
}

Answer 2

For finding out the minimum you can use:

auto result = std::min_element(enemies.begin(), enemies.end(), [](auto a, auto b){return a->rect.getPosition()< b->rect.getPosition();});
std::cout<<"minimum is: "<<(**result).rect.getPosition()<<std::endl;

The above example will print out the position of the closest(minimum) enemy as you want.