如何有效地从给定另一个向量的向量中删除元素 [英] How to efficiently delete elements from a vector given an another vector

问题描述

在给定另一个向量的向量中删除元素的最好方法是什么？

What is the best way to delete elements from a vector given an another vector?

我想出了以下代码：

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

void remove_elements(vector<int>& vDestination, const vector<int>& vSource) 
{
    if(!vDestination.empty() && !vSource.empty())
    {
        for(auto i: vSource) {
            vDestination.erase(std::remove(vDestination.begin(), vDestination.end(), i), vDestination.end());
        }
    }
}

int main() 
{
    vector<int> v1={1,2,3};
    vector<int> v2={4,5,6};
    vector<int> v3={1,2,3,4,5,6,7,8,9};
    remove_elements(v3,v1);
    remove_elements(v3,v2);
    for(auto i:v3)
        cout << i << endl;
    return 0;
}

这里的输出将是：

7
8
9

推荐答案

我的版本如下，我只应用擦除 已移动到 std :: remove 的末尾，并跟踪指向向量结尾的指针 vDestination 不对其进行迭代。

My version is the following, I only apply erase after all elements from the vector vSource have been moved to the end by std::remove and keep track of the pointer to the end of the vector vDestination to not iterate over it for nothing.

void remove_elements(vector<int>& vDestination, const vector<int>& vSource) 
{
    auto last = std::end(vDestination);
    std::for_each(std::begin(vSource), std::end(vSource), [&](const int & val) {
        last = std::remove(std::begin(vDestination), last, val);
    });
    vDestination.erase(last, std::end(vDestination));
}

查看coliru：http://coliru.stacked-crooked.com/a/6e86893babb6759c

更新

这里是一个模板版本，所以你不关心容器类型：

Here is a template version, so you don't care about the container type :

template <class ContainerA, class ContainerB>
void remove_elements(ContainerA & vDestination, const ContainerB & vSource) 
{
    auto last = std::end(vDestination);
    std::for_each(std::begin(vSource), std::end(vSource), [&](typename ContainerB::const_reference val) {
        last = std::remove(std::begin(vDestination), last, val);
    });
    vDestination.erase(last, std::end(vDestination));
}

---

/ strong>

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Note

此版本适用于没有任何约束的向量，如果你的向量被排序，你可以采取一些快捷方式，避免迭代遍历向量删除每个元素。

This version works for vectors without any constraints, if your vectors are sorted you can take some shortcuts and avoid iterating over and over the vector to delete each element.

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