STL--集合：set

set的介绍

       set就是数学上的集合--每个元素最多只出现一次。和sort一样，自定义类型也可以构造set，但同样必须定义“小于”运算符。set中元素具有已从小到大排好序的性质。

set的应用

题目

       输入一个文本，找出所有不同的单词（连续的字母序列），按字典序从小到大输出。单词不区分大小写。

样例输入

Adventures in Disneyland Two blondes were going to Disneyland
when they came to a fork in the road. The sign read: “Disneyland
Left.” So they went home.

样例输出

a
adventures
blondes
came
disneyland
fork
going
home
in
left
read
road
sign
so
the
they
to
two
went
were
when

代码

#include<iostream>
#include<string>
#include<set>
#include<sstream>
using namespace std;
set<string>dict;//string集合
int main(){
	string s,buf;
	while(cin>>s){
		for(int i=0;i<s.length();i++){
			if(isalpha(s[i])){//判断是否为字母 
				s[i]=tolower(s[i]);
			}
			else{
				s[i]=' ';
			}
		}
		stringstream ss(s);//字符串流处理 
		while(ss>>buf){//导出到buf 
			dict.insert(buf);
		}
	}
	for(set<string>::iterator it=dict.begin();it!=dict.end();++it){//iterator为迭代器，类似于指针 
		cout<<*it<<"\n";
	} 
	return 0;
}