Union, intersection, and difference set of set in STL

The set key is automatically sorted, and the corresponding intersection of the Union set difference sets can all use this ordered feature. The time complexity is O (m + n), m, n is the size of the two containers.

1. set_union can be used to calculate the union of two sets. It is a stable operation because the relative positions between elements do not change.

The source code is as follows:

Template <Class Identifier, class inputiterator2, class outputiterator> outputiterator set_union (extends first1, extends last1, extends first2, inputiterator2 last2, outputiterator result! = Last1 & first2! = Last2) {If (* first1 <* first2) {* result = * first1; ++ first1;} else if (* first1> * first2) {* result = * first2; + + first2;} else // equal case {* result = * first1; ++ first1; ++ first2 ;}++ result ;}return copy (first2, last2, copy (first1, last1, result ));}

2. set_intersection can be used to calculate the intersection of two sets.

The source code is as follows:

Template <Class Identifier, Class Identifier, class outputiterator> outputiterator set_intersection (Response first1, response last1, response first2, inputiterator2 last2, outputiterator result) {While (first1! = Last1 & first2! = Last2) {If (* first1 <* first2) {++ first1;} else if (* first1> * first2) {++ first2 ;} else {// * first1 = * first2, which is the intersection element * result = * first1; ++ first1; ++ first2; ++ result ;}} return result ;}

3. set_diference is used to calculate the difference set of two sets.

The source code is as follows:

Template <Class Identifier, Class Identifier, class outputiterator> outputiterator set_difference (partition first1, partition last1, partition first2, inputiterator2 last2, outputiterator result) {While (first1! = Last1 & first2! = Last2) {If (* first1 <* first2) // * first1 <* first2, which is the element of the difference set {* result = * first1; ++ first1; + + result;} else if (* first1> * first2) ++ first2; else {++ first1; ++ first2 ;}} return copy (first1, last1, result );}

Simple test:

# Include <iostream> # include <cstdlib> # include <set> # include <algorithm> # include <vector> using namespace STD; int main () {set <int> S1, s2; s1.insert (1); s1.insert (2); s1.insert (3); s2.insert (2); s2.insert (3); s2.insert (4); set <int> :: iterator iter1 = s1.begin (); set <int >:: iterator iter2 = s1.end (); set <int >:: iterator iter3 = s2.begin (); set <int> :: iterator iter4 = s2.end (); vector <int> res (10, 0); vector <int>: iterator ITER; iter = set_union (iter1, iter2, iter3, iter4, Res. begin (); // Union // iter = set_intersection (iter1, iter2, iter3, iter4, Res. begin (); // intersection // iter = set_difference (iter1, iter2, iter3, iter4, Res. begin (); // difference set res. resize (iter-res.begin (); For (iter = res. begin (); iter! = Res. End (); ++ ITER) {cout <* ITER <Endl;} system ("pause"); Return 0 ;}

Union, intersection, and difference set of set in STL