温故而知新-set

set：同map一样，关联式容器。在插入时就会进行排序，主要特点如下：

1、记录元素即是key值又是value值

2、插入的时候严格排序，底层是红黑树

3、删除元素时只要操作指针节点，无需进行内存的拷贝和移动。

#include <iostream>
#include <set>
using namespace std;
int main(int argc, char *argv[]) {
	std::set<int> myset;
	std::set<int>::iterator it;
	std::pair<std::set<int>::iterator,bool> ret;
	// set some initial values:
	for (int i=1; i<=5; ++i){
	 	myset.insert(i*10);    // set: 10 20 30 40 50
	}
	ret = myset.insert(20);               // no new element inserted
	if (ret.second==false){
		it=ret.first;  // "it" now points to element 20
		std::cout<<"now points to element to: "<<*it<<std::endl;
	} 
	myset.insert (it,25);                 // max efficiency inserting
	myset.insert (it,24);                 // max efficiency inserting
	myset.insert (it,26);                 // no max efficiency inserting
	int myints[]= {5,10,15};              // 10 already in set, not inserted
	myset.insert (myints,myints+3);
	std::cout << "myset contains:";
	for (it=myset.begin(); it!=myset.end(); ++it){
		std::cout << ' ' << *it;
	}
	std::cout << '\n';
	std::cout<<"let's find element 40...."<<std::endl;
	it = myset.find(50);
	if(it!=myset.end())
	{
		std::cout<<"find element 50: "<<*it<<std::endl;
	}
	return 0;
}