第六章：算法之set
set相关算法
STL提供了四种与set相关的算法，分别是并集（union）、交集（intersection）、差集（difference）和对称差集（symmetric difference），这4个算法接受的set必须是有序区间，都至少接受4个参数，分别表示两个set区间。所谓的set可细分为数学上的定义和STL的定义两种，数学上的set允许元素重复而未经排序，；例如{1,5,5,3,2}，STL的定义要求元素不得重复，且必须经过排序，例如{1,3,5,6}。
测试程序如下：
#include <set> // multiset
#include <iostream>
#include <algorithm>
#include <iterator> // ostream_iterator
using namespace std;
template <class T>
struct display {
void operator() (const T& x) {
cout << x << ' ';
}
};
int main() {
int ia1[6] = {1, 3, 5, 7, 9, 11};
int ia2[7] = {1, 1, 2, 3, 5, 8, 13};
multiset<int> S1(ia1, ia1 + 6);
multiset<int> S2(ia2, ia2 + 7);
for_each(S1.begin(), S1.end(), display<int>());
cout << endl;
for_each(S2.begin(), S2.end(), display<int>());
cout << endl;
auto first1 = S1.begin();
auto last1 = S1.end();
auto first2 = S2.begin();
auto last2 = S2.end();
cout << "Union of S1 and S2: ";
set_union(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
cout << endl;
first1 = S1.begin();
first2 = S2.begin();
cout << "Intersection of S1 and S2: ";
set_intersection(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
cout << endl;
first1 = S1.begin();
first2 = S2.begin();
cout << "Difference of S1 and S2(S1-S2): ";
set_difference(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
cout << endl;
first1 = S1.begin();
first2 = S2.begin();
cout << "Symmetric difference of S1 and S2: ";
set_symmetric_difference(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
cout << endl;
first1 = S2.begin();
first2 = S1.begin();
last1 = S2.end();
last2 = S1.end();
cout << "Difference of S2 and S1(S2-S1): ";
set_difference(first1, last1, first2, last2, ostream_iterator<int>(cout, " "));
cout << endl;
return 0;
}
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执行结果：
[root@192 6_STL_algorithms]# ./6_5_set-algorithms
1 3 5 7 9 11
1 1 2 3 5 8 13
Union of S1 and S2: 1 1 2 3 5 7 8 9 11 13
Intersection of S1 and S2: 1 3 5
Difference of S1 and S2(S1-S2): 7 9 11
Symmetric difference of S1 and S2: 1 2 7 8 9 11 13
Difference of S2 and S1(S2-S1): 1 2 8 13
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