C++ STL 集合运算
定义于头文件<algorithm>的算法：
集合运算的前提是两个集合必须按照同样的规则排序就绪，否则不能进行集合运算!
- map,set是有序集合,可以直接参加运算;vector是无序集合,参与运算前必须首先排序.
template< class InputIt1, class InputIt2, class OutputIt >
前两个参数是输入参数，代表参与集合运算的两个集合，最后一个是输出参数，输出运算结果(**也是相同排序规则的集合**)。
- 交集(set_intersection)
OutputIt set_intersection( InputIt1 first1, InputIt1 last1,InputIt2 first2, InputIt2 last2, OutputIt d_first ); - 并集(set_union)
OutputIt set_union( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first ); - 差集(set_difference)
OutputIt set_difference( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first ); - 对称差集(set_symmetric_difference)
OutputIt set_symmetric_difference( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first ); - 如果使用比较函数，末尾再追加一个参数，用法见示例.
附完整示例代码
#include "stdafx.h"
#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <algorithm>
#include <iterator>
/***************************************************
* map key compare
* include compare string's length
* 用于排序map的keys，如："P1","P2","P10",...
* 用法：
* （1）map键值排序：map<string,int,cmpByKey> map1;
* （2）set排序: set<string,cmpByKey> set1;
* （3）vector<string>排序：
* #include <algorithm>
* vector<string> vec1;
* std::sort(vec1.begin(), vec1.end(), cmpByKey());
****************************************************/
struct cmpByKey {
bool operator()(const std::string& lhs, const std::string& rhs) const
{
bool ret;
if (lhs.size() == rhs.size())
ret = lhs < rhs ? true : false;
else
ret = lhs.size() < rhs.size() ? true : false;
return ret;
}
};
using namespace std;
// 使用默认比较函数less<>排序
int main1()
{
std::vector<int> v1{ 1,2,3,4,5,6,7,8 };
std::vector<int> v2{ 5, 7, 9,10 };
std::sort(v1.begin(), v1.end()); // 升序排序,默认使用less<int>比较函数
std::sort(v2.begin(), v2.end());
// A交B
cout << "set_intersection:" << endl;
std::vector<int> v_intersection;
std::set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(v_intersection));
for (int n : v_intersection) std::cout << n << ' '; cout << endl; // 5 7
// A并B
cout << "set_union" << endl;
std::vector<int> dest1;
std::set_union(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(dest1));
for (const auto &i : dest1) std::cout << i << ' '; std::cout << '\n'; // 1 2 3 4 5 6 7 8 9 10
// A - B
cout << "set_difference" << endl;
std::vector<int> diff;
std::set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(diff));
for (int n : diff) std::cout << n << ' '; cout << endl; // 1 2 3 4 6 8
// 对称差(symmetric_difference,A并B - A交B)
cout << "set_symmetric_difference" << endl;
std::vector<int> v_symDifference;
std::set_symmetric_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(v_symDifference));
for (int n : v_symDifference) std::cout << n << ' '; // 1 2 3 4 6 8 9 10
cout << endl;
system("pause");
return 0;
}
// 使用非默认比较函数
int main()
{
std::vector<int> v1{ 1,2,3,4,5,6,7,8 };
std::vector<int> v2{ 5, 7, 9,10 };
//std::sort(v1.begin(), v1.end()); // 升序排序,默认使用less<int>比较函数
//std::sort(v2.begin(), v2.end());
// 采用非默认比较函数，
std::sort(v1.begin(), v1.end(), greater<int>()); // 降序排序
std::sort(v2.begin(), v2.end(), greater<int>());
// 集合运算必须与集合的排序规则一致，因此最后一个参数需设置比较函数
// A交B
cout << "set_intersection:" << endl;
std::vector<int> v_intersection;
std::set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(v_intersection),greater
<int>());
for (int n : v_intersection) std::cout << n << ' '; cout << endl; // 7 5
// A并B
cout << "set_union" << endl;
std::vector<int> dest1;
std::set_union(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(dest1),greater<int>());
for (const auto &i : dest1) std::cout << i << ' '; std::cout << '\n'; // 10 9 8 7 6 5 4 3 2 1
// A - B
cout << "set_difference" << endl;
std::vector<int> diff;
std::set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(diff),greater<int>());
for (int n : diff) std::cout << n << ' '; cout << endl; // 8 6 4 3 2 1
// 对称差(symmetric_difference,A并B - A交B)
cout << "set_symmetric_difference" << endl;
std::vector<int> v_symDifference;
std::set_symmetric_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), std::back_inserter(v_symDifference),greater<int>());
for (int n : v_symDifference) std::cout << n << ' '; // 10 9 8 6 4 3 2 1
cout << endl;
set<string, cmpByKey> set1 = { "P1","P10","P3","P20" };
set<string, cmpByKey> set2 = { "P10","P2" };
set<string, cmpByKey> results;
/******** 编译出错，修改为下句 *********/
//std::set_intersection(set1.begin(), set1.end(), set2.begin(), set2.end(), std::back_inserter(results), cmpByKey());
std::set_intersection(set1.begin(), set1.end(), set2.begin(), set2.end(), std::inserter(results, results.end()), cmpByKey());
for (string s : results) std::cout << s << ' '; cout << endl; // P10
results.clear();
std::set_union(set1.begin(), set1.end(), set2.begin(), set2.end(), std::inserter(results, results.end()), cmpByKey());
for (string s : results) std::cout << s << ' '; cout << endl; // P1 P2 P3 P10 P20
results.clear();
std::set_difference(set1.begin(), set1.end(), set2.begin(), set2.end(), std::inserter(results, results.end()), cmpByKey());
for (string s : results) std::cout << s << ' '; cout << endl; // P1 P3 P20
results.clear();
std::set_symmetric_difference(set1.begin(), set1.end(), set2.begin(), set2.end(), std::inserter(results, results.end()), cmpByKey());
for (string s : results) std::cout << s << ' '; cout << endl; // P1 P2 P20
system("pause");
return 0;
}