C++Primer第五版——习题答案详解（十）
习题答案目录：https://www.cnblogs.com/Mered1th/p/10485695.html
第11章 关联容器
练习11.3
#include<iostream>
#include<string>
#include<map>
using namespace std;
int main() {
string s;
map<string, size_t> num;
cout << "输入单词表：" << endl;
while (cin >> s) {
++num[s];
}
for (const auto &i : num) {
cout << i.first << " occurs " << i.second << ((i.second > 1) ? " times" : " time") << endl;
}
system("pause");
return 0;
}
练习11.4
#include<iostream>
#include<string>
#include<map>
#include<cctype>
using namespace std;
void process(string &s) {
for (auto i = 0;i < s.size(); ++i) {
if (isupper(s[i])) s[i] = tolower(s[i]);
else if (ispunct(s[i])) {
s.erase(i,1);
}
}
}
int main() {
string s;
map<string, size_t> num;
cout << "输入单词表：" << endl;
while (cin >> s) {
process(s);
++num[s];
}
for (const auto &i : num) {
cout << i.first << " occurs " << i.second << ((i.second > 1) ? " times" : " time") << endl;
}
system("pause");
return 0;
}
练习11.7
#include<map>
#include<vector>
#include<iostream>
#include<string>
using namespace std;
int main() {
map<string, vector<string>> mp;
string last_name, first_name;
cout << "输入姓：" << endl;
cin >> last_name;
cout << "输入该姓的成员名字：" << endl;
while (cin >> first_name) {
mp[last_name].push_back(first_name);
}
for (const auto i : mp) {
cout << "姓：" << i.first << " 有以下成员：" << endl;
for (const auto j : i.second) {
cout << j << " ";
}
cout << endl;
}
system("pause");
return 0;
}
练习11.8
#include<vector>
#include<iostream>
#include<algorithm>
using namespace std;
int main() {
vector<int> v = { 1,1,2,3,4,4,5,6 };
auto iter = unique(v.begin(), v.end());
v.erase(iter, v.end());
for (auto i : v) {
cout << i << " ";
}
cout << endl;
system("pause");
return 0;
}
练习11.9
map<string, list<size_t>> mp;
练习11.10
vector可以，因为定义了比较大小的操作，list未定义所以不行。
练习11.11
using compareType = bool (*)(const Sales_data& lhs, const Sales_data& rhs);
练习11.12
#include<vector>
#include<utility>
#include<iostream>
#include<string>
using namespace std;
int main() {
vector<pair<string,int>> vec;
size_t i = 0;
string s;
int num;
while (cin >> s >> num) {
vec.push_back({ s,num });
++i;
}
for (auto i : vec) {
cout << i.first << " " << i.second << endl;
}
system("pause");
return 0;
}
练习11.13
#include<vector>
#include<utility>
#include<iostream>
#include<string>
using namespace std;
int main() {
vector<pair<string,int>> vec;
size_t i = 0;
string s;
int num;
while (cin >> s >> num) {
//vec.push_back({ s,num }); 第一种
vec.emplace_back(s, num); //第二种：最简便
//vec.push_back(make_pair(str,i));//第三种
++i;
}
for (auto i : vec) {
cout << i.first << " " << i.second << endl;
}
system("pause");
return 0;
}
练习11.14
#include<map>
#include<vector>
#include<iostream>
#include<string>
#include<utility>
using namespace std;
int main() {
map<string, vector<pair<string,string>>> mp;
string last_name, first_name, birthday;
cout << "输入姓：" << endl;
cin >> last_name;
cout << "输入该姓的成员名字和生日：" << endl;
while (cin >> first_name >> birthday) {
mp[last_name].emplace_back(first_name, birthday);
}
for (const auto i : mp) {
cout << "姓：" << i.first << " 有以下成员：" << endl;
for (const auto j : i.second) {
cout << j.first << " " << j.second << endl;
}
cout << endl;
}
system("pause");
return 0;
}
练习11.15
mapped_type 是vector
key_type 是int
value_type 是pair<int,vector
练习11.16
#include<map>
#include<iostream>
#include<string>
using namespace std;
int main() {
map<string, int> mp;
mp["aaa"] = 1;
auto iter = mp.begin();
iter->second = 2;
//iter->first = "bbb"; const 不允许修改
cout << iter->first << " " << iter->second << endl;
system("pause");
return 0;
}
练习11.17
第三个不合法，back_inserter()需要用到push_back()，而set没有；其余合法。
练习11.18
map<const string,size_t>::iterator
练习11.19
using compareType = bool (*)(const Sales_data &lhs, const Sales_data &rhs);
multiset<Sales_data, compareType> bookstore(compareIsbn);
multiset<Sales_data, compareType>::iterator c_it = bookstore.begin();
练习11.20
#include<iostream>
#include<string>
#include<map>
using namespace std;
int main() {
map<string, size_t> word_count;
string word;
while (cin >> word) {
auto ret = word_count.insert({ word,1 });
if (!ret.second) {
++ret.first->second;
}
}
for (auto i : word_count) {
cout << i.first << " " << i.second << endl;
}
system("pause");
return 0;
}
之前的更容易阅读和编写。
练习11.21
word_count.insert({ word,0 }) //得到insert的返回值，是一个pair
word_count.insert({ word,0 }).first //是pair的第一个成员，是一个map迭代器，指向具有给定关键字的元素
word_count.insert({ word,0 }).first -> //解引用此迭代器，提取map中的元素，元素也是一个pair
word_count.insert({ word,0 }).first -> second //map中元素的值部分
++word_count.insert({ word,0 }).first->second //递增此值
练习11.23
#include<map>
#include<vector>
#include<iostream>
#include<string>
using namespace std;
int main() {
multimap<string, vector<string>> mp;
vector<string> vs;
string last_name, first_name;
cout << "总共有几个姓：" << endl;
int n, k = 1;
cin >> n;
while (n--) {
cout << "请输入第" << k << "个姓：" << endl;
cin >> last_name;
cout << "请输入姓" << last_name << "的成员,并以 END 结束当前输入" << endl;
while (cin >> first_name) {
if(first_name!="END") vs.push_back(first_name);
else break;
}
mp.insert({ last_name,vs });
k++;
}
for (const auto i : mp) {
cout << "姓：" << i.first << " 有以下成员：";
for (const auto j : i.second) {
cout << j << " ";
}
cout << endl;
}
system("pause");
return 0;
}
练习11.28
#include<iostream>
#include<string>
#include<vector>
#include<map>
using namespace std;
int main() {
map<string, vector<int>> mp = { { "aa",{1,2,3,4} } };
auto iter = mp.find("aa");
cout << iter->first << endl;
system("pause");
return 0;
}
练习11.29
upper_bound和lower_bound返回相等的迭代器——指向一个不影响排序的关键字插入位置。
练习11.30
第一个迭代器引用后得到书名。
练习11.31
#include<iostream>
#include<map>
#include<string>
using namespace std;
int main() {
string search_item = "bbb";
multimap < string, string > mp = { {"John", "aaa"}, { "John","bbb" }, { "John","ccc" },{"Tom","ddd"} };
auto iter = mp.find("John");
auto num = mp.count("John");
while (num) {
if (iter->second == search_item) {
mp.erase(iter);
break;
}
++iter;
--num;
}
for (auto i : mp) {
cout << i.first << " " << i.second << endl;
}
system("pause");
return 0;
}
练习11.32
#include<iostream>
#include<map>
#include<string>
#include<set>
using namespace std;
int main() {
string search_item = "bbb";
multimap < string, string > mp = { {"John", "baa"}, { "John","abb" }, { "John","ced" },{"Tom","ccc"},{"Bob","zzz"},{"Bob","aae"} };
map<string, set<string>> ans;
for (auto i : mp) {
ans[i.first].insert(i.second);
}
for (auto i : ans) {
cout << i.first << " : ";
for (auto j : i.second) {
cout << j << " ";
}
cout << endl;
}
system("pause");
return 0;
}
练习11.33
#include<iostream>
#include<string>
#include<map>
#include<fstream>
#include<sstream>
using namespace std;
//函数buildMap读入给定文件，建立起转换映射
map<string, string> buildMap(ifstream &map_file) {
map<string, string> trans_map;
string key;
string value;
//读取第一个单词存入key中，行中剩余内容存入value
while (map_file >> key && getline(map_file, value)) {
if (value.size() > 1) {
trans_map[key] = value.substr(1); //跳过前导空格
}
else {
throw runtime_error("no rule for " + key);
}
}
return trans_map;
}
//生成文本转换
const string & transform(const string &s, const map<string, string> &m) {
auto map_it = m.find(s);
if (map_it != m.cend()) {
return map_it->second;
}
else {
return s;
}
}
void word_transform(ifstream &map_file, ifstream &input) {
auto trans_map = buildMap(map_file);//保存转换规则
string text;
while (getline(input, text)) {
istringstream stream(text); //读取每个单词
string word;
bool firstword = true; //控制是否打印空格
while (stream >> word) {
if (firstword) {
firstword = false;
}
else cout << " ";
//transform返回它的第一个参数或其转换之后的形式
cout << transform(word, trans_map);
}
cout << endl;
}
}
int main() {
ifstream map_file("book.txt"), input("test.txt");
word_transform(map_file, input);
system("pause");
return 0;
}
练习11.34
下标操作，当元素不存在时会隐式地创建一个新元素插入到map中，修改了map
练习11.35
如果有重复的key，则下标表示时新的会替换旧的，而insert不会，那么在transform函数中find会有多个返回值导致出错。
练习11.36
#include<iostream>
#include<string>
#include<map>
#include<fstream>
#include<sstream>
using namespace std;
//函数buildMap读入给定文件，建立起转换映射
map<string, string> buildMap(ifstream &map_file) {
map<string, string> trans_map;
string key;
string value;
//读取第一个单词存入key中，行中剩余内容存入value
while (map_file >> key && getline(map_file, value)) {
if (value.size() > 1) {
trans_map[key] = value.substr(1); //跳过前导空格
}
else {
throw runtime_error("no rule for " + key);
}
}
return trans_map;
}
//生成文本转换
const string & transform(const string &s, const map<string, string> &m) {
auto map_it = m.find(s);
if (map_it != m.cend()) {
return map_it->second;
}
else {
return s;
}
}
void word_transform(ifstream &map_file, ifstream &input) {
auto trans_map = buildMap(map_file);//保存转换规则
string text;
while (getline(input, text)) {
istringstream stream(text); //读取每个单词
string word;
bool firstword = true; //控制首个空格
while (stream >> word) {
if (firstword) {
firstword = false;
}
else cout << " ";
//transform返回它的第一个参数或其转换之后的形式
cout << transform(word, trans_map);
}
cout << endl;
}
}
int main() {
ifstream map_file("book.txt"), input("test.txt");
word_transform(map_file, input);
system("pause");
return 0;
}
练习11.37
无序容器不用排序，效率高。
有序容器可以自定义排序。
练习11.38
单词计数程序
#include <unordered_map>
#include <string>
#include <iostream>
using namespace std;
int main()
{
unordered_map<string, size_t> word_count;
string word;
while(cin >> word)
++word_count[word];
for(const auto &w : word_count)
cout << w.first << "," << w.second << endl;
return 0;
}
单词转换程序
#include<iostream>
#include<string>
#include<unordered_map>
#include<fstream>
#include<sstream>
using namespace std;
//函数buildMap读入给定文件，建立起转换映射
unordered_map<string, string> buildMap(ifstream &map_file) {
unordered_map<string, string> trans_map;
string key;
string value;
//读取第一个单词存入key中，行中剩余内容存入value
while (map_file >> key && getline(map_file, value)) {
if (value.size() > 1) {
trans_map[key] = value.substr(1); //跳过前导空格
}
else {
throw runtime_error("no rule for " + key);
}
}
return trans_map;
}
//生成文本转换
const string & transform(const string &s, const unordered_map<string, string> &m) {
auto map_it = m.find(s);
if (map_it != m.cend()) {
return map_it->second;
}
else {
return s;
}
}
void word_transform(ifstream &map_file, ifstream &input) {
auto trans_map = buildMap(map_file);//保存转换规则
string text;
while (getline(input, text)) {
istringstream stream(text); //读取每个单词
string word;
bool firstword = true; //控制首个空格
while (stream >> word) {
if (firstword) {
firstword = false;
}
else cout << " ";
//transform返回它的第一个参数或其转换之后的形式
cout << transform(word, trans_map);
}
cout << endl;
}
}
int main() {
ifstream map_file("book.txt"), input("test.txt");
word_transform(map_file, input);
system("pause");
return 0;
}
