C++ map 总结

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/CV2017/article/details/85872465

注：看《C++ Primer 5》的笔记，不定期更新

map 是什么

map 是一种数据结构，是关键字-值对的集合，称为关联容器

map 实现单词计数程序

#include <iostream>
#include <map>
#include <string>

using namespace std;

void wordCound(map<string, size_t> word_count)
{
	for (const auto &w : word_count)
	{
		cout << w.first << " occurs " << w.second << ((w.second > 1) ? " times" : " time") << endl;
	}
}

int main()
{
	map<string, size_t> word_count;
	string word;
	while (cin >> word)
	{
		++word_count[word];
	}

	wordCound(word_count);

	return 0;
}

提示：windows 平台下输入几个单词后，先按回车，再按 ctrl + z，再按回车

map 与 set 实现单词计数程序

#include <iostream>
#include <map>
#include <set>
#include <string>

using namespace std;

void wordCound(map<string, size_t> word_count)
{
	for (const auto &w : word_count)
	{
		cout << w.first << " occurs " << w.second << ((w.second > 1) ? " times" : " time") << endl;
	}
}

int main()
{
	map<string, size_t> word_count;

	set<string> exclude = { "The", "But", "And", "Or" };

	string word;

	while (cin >> word)
	{
		if (exclude.find(word) == exclude.end())
		{
			++word_count[word];
		}	
	}

	wordCound(word_count);

	return 0;
}

map 实现忽略大小写和标点的单词计数程序

#include <iostream>
#include <map>
#include <set>
#include <string>

using namespace std;

string& trans(string &s)
{
	for (int p = 0; p < s.size(); p++)
	{
		if (s[p] >= 'A' && s[p] <= 'Z')
		{
			s[p] += 32;
		}
		else if (s[p] == ',' || s[p] == '.')
		{
			s.erase(p, 1);
		}
	}

	return s;
}

void wordCound(map<string, size_t> word_count)
{
	for (const auto &w : word_count)
	{
		cout << w.first << " occurs " << w.second << ((w.second > 1) ? " times" : " time") << endl;
	}
}

int main()
{
	map<string, size_t> word_count;

	set<string> exclude = { "The", "But", "And", "Or" };

	string word;

	while (cin >> word)
	{
		if (exclude.find(word) == exclude.end())
		{
			++word_count[trans(word)];
		}	
	}

	wordCound(word_count);

	return 0;
}

map 含 vector 实现添加

#include <iostream>
#include <map>
#include <vector>
#include <string>

using namespace std;

void addFamily(map<string, vector<string>> &families, const string &family)
{
	if (families.find(family) == families.end())
	{
		families[family] = vector<string>(); //创建空的 vector
	}
}

void addChild(map<string, vector<string>> &families, const string &family, const string &child)
{
	families[family].push_back(child);
}

int main()
{
	map<string, vector<string>> families;

	addFamily(families, "王");

	addChild(families, "王", "鑫");

	addChild(families, "王", "一丁");

	addFamily(families, "张");

	for (auto f : families)
	{
		cout << f.first << " 家的孩子：";

		for (auto c : f.second)
		{
			cout << c << " ";
		}

		cout << endl;
	}

	return 0;
}

 

map 与 vector 的区别

https://blog.csdn.net/CV2017/article/details/85222426

map 与 set 区别

map 是一对关键字-值的存储容器，set 是单个关键字即值的存储

map 适用场景

map 适合对一些对象按它们的某个特征进行访问，比如按学生的名字来查询学生信息，将学生名字作为关键字，学生信息作为元素值