STL(标准模板库)笔记——平衡二叉树map

STL(标准模板库)笔记---平衡二叉树map

本系列是观看北大郭炜老师程序与算法课程的笔记，用于复习与巩固。

map

map的用法

和multimap区别在于：

• 不能有关键字重复的元素
• 可以使用 [] ，下标为关键字，返回值为first和关键字相同的元 素的second
• 插入元素可能失败

#include <iostream> 
#include <map> 
#include <string> 
using namespace std; 
struct Student { 
	string name; 
	int score; 
}; 
Student students[5] = {
 {"Jack",89},{"Tom",74},{"Cindy",87},{"Alysa",87},{"Micheal",98}}; 
 typedef map<string,int> MP; 
 int main() 
 {
 	MP mp; 
 	for(int i = 0;i < 5; ++i) 
 		mp.insert(make_pair(students[i].name,students[i].score)); 
 	cout << mp["Jack"] << endl;  // 输出 89 
 	mp["Jack"] = 60; //修改名为"Jack"的元素的second 
	for(MP::iterator i = mp.begin(); i != mp.end(); ++i) 
		cout << "(" << i->first << "," << i->second << ") "; 
		//输出：(Alysa,87) (Cindy,87) (Jack,60) (Micheal,98) (Tom,74) 
		cout << endl; 
		Student st; 
		st.name = "Jack"; 
		st.score =  99; 
		pair<MP::iterator, bool> p = mp.insert(make_pair(st.name,st.score)); 
		if( p.second ) 
			cout << "(" << p.first->first << "," << p.first->second << ") inserted" <<endl; 
		else cout << "insertion failed" << endl; //输出此信息 
		mp["Harry"] = 78; //插入一元素，其first为"Harry",然后将其second改为78 
		MP::iterator q = mp.find("Harry"); 
		cout << "(" << q->first << "," << q->second <<")" <<endl; //输出 (Harry,78) 
		return 0; 
}

map例题：单词词频统计程序

输入大量单词，每个单词，一行，不超过20字符，没有 空格。 按出现次数从多到少输出这些单词及其出现次数 。出现次数相同的，字典序靠前的在前面

输入样例：
this 
is 
ok 
this 
plus 
that 
is 
plus 
plus
输出样例：
plus 3 
is 2 
this 2 
ok 1 
that 1

#include <iostream> 
#include <set> 
#include <map> 
#include <string> 
using namespace std; 
struct Word { 
	int times; 
	string wd; 
}; 
struct Rule { 
	bool operator () ( const Word & w1,const Word & w2) const { 
		if( w1.times != w2.times) 
			return w1.times > w2.times; 
		else return w1.wd < w2.wd; 
		} 
};
int main() 
{ 
	string s; 
	set<Word,Rule> st; 
	map<string,int> mp; 
	while( cin >> s ) 
		++ mp[s] ; 
	for( map<string,int>::iterator i = mp.begin(); i != mp.end(); ++i) { 
		Word tmp; 
		tmp.wd = i->first; 
		tmp.times = i->second; 
		st.insert(tmp); 
	} 
	for(set<Word,Rule>::iterator i = st.begin(); 
		i != st.end(); ++i) 
	cout << i->wd << " " << i->times << endl; 
}