c++primer第五版第十章练习

10.1

#include <iostream>#include <algorithm>//count#include <vector>int main(){using namespace std;vector<int> vec = { 4, 9, 3, 5, 8, 6, 6, 5, 4 };cout << count(vec.begin(), vec.end(), 4);//统计4在vec元素里出现的次数system("pause");return 0;}

10.2

#include <iostream>#include <algorithm>//count#include <list>#include <string>int main(){using namespace std;list<string> lstr = { "c++", "main", "visual", "studio", "c++", "false", "true", "c++", "string", "c++" };cout << "c++:" << count(lstr.begin(), lstr.end(), "c++");//统计"c++"字符串在lstr中出现的次数system("pause");return 0;}

10.3

#include <iostream>#include <vector>#include <numeric>//accumulate()int main(){using namespace std;vector<int> vec = { 4, 8, 5, 2, 1, 4, 7, 8, 9, 6, 3, 2 };cout << accumulate(vec.begin(), vec.end(), 0);//计算vec中元素之和，0为初始值system("pause");return 0;}

10.4

accumulate第三个参数的值的类型，表示容器元素转换为对应的类型，那么如果元素是double，转换为int后精度就会丢失。

10.5

一样，但是char *编译器可能会警告，或许用const char *会更好

10.6

#include <iostream>#include <vector>#include <algorithm>//fill_nint main(){using namespace std;vector<int> vi = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };for (auto x : vi)cout << x << "\t";fill_n(vi.begin(), vi.size(), 0);//把vi中所有元素的值设为0for (auto x : vi)cout << x << "\t";system("pause");return 0;}

10.7

a vec是空的，使用copy时要确保至少与输入队列同样多的元素

修改为：copy(lst.cbegin(),lst.cend(),back_iterator(vec));

b 虽然是没错，但是也没任何一样，.size()是0，因为里面没有元素，reservr只是分配预存空间，不添加元素

修改为：vec.resize()或者是fill_n(back_iterator(vec),10,0);

10.8

back_iterator是定义在iterator文件里的，而且算法只是执行这一过程，所以与算法无关。

10.9

#include <iostream>#include <vector>#include <algorithm>//sort unique#include <string>void elimDups(std::vector<std::string> &vstr){sort(vstr.begin(),vstr.end());//排序默认小到大auto u_end = unique(vstr.begin(), vstr.end());//删除连续重复的元素vstr.erase(u_end, vstr.end());//清理空元素}int main(){using namespace std;vector<string> vstr = { "111", "222", "333", "444", "222", "333", "555", "777", "111", "888", "666", "666", "999" };elimDups(vstr);for (auto s : vstr)cout << s << endl;system("pause");return 0;}

10.10

个人认为是为了区分算法和成员函数的操作，而且改变后会使迭代器失效

网上找的答案：因为标准库算法操作的迭代器，而不是容器。因此，算法不能（直接）添加或删除元素。（大雾不太明）

10.11

#include <iostream>#include <vector>#include <algorithm>//stable_sort unique#include <string>bool isShorter(const std::string &s1, const std::string &s2){return s1.size() > s2.size();}void elimDups(std::vector<std::string> &vstr,bool (*p)(const std::string &s1,const std::string &s2)){sort(vstr.begin(), vstr.end());//按默认排序stable_sort(vstr.begin(), vstr.end(), p);//按照谓词p的条件来排序相同长度的单词auto u_end = unique(vstr.begin(), vstr.end());//删除连续相同的元素vstr.erase(u_end, vstr.end());//清空删除后留下的空白}int main(){using namespace std;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete" };elimDups(vstr,isShorter);for (auto s : vstr)cout << s << endl;system("pause");return 0;}

10.12

#include "../../7.21/7.21/标头.h"#include <vector>#include <algorithm>//sortbool compareIsbn(Sales_data &v1, Sales_data &v2){return v1.isbn().size() < v2.isbn().size();}int main(){using namespace std;vector<Sales_data> vsd;Sales_data temp;while (read(cin, temp))vsd.push_back(temp);sort(vsd.begin(), vsd.end(), compareIsbn);//按照谓词compareIsbn来排序for (auto &x : vsd)cout << x.isbn() << endl;system("pause");return 0;}

10.13

#include <iostream>#include <string>#include <vector>#include <algorithm>//partition for_eachbool isShorter(const std::string &s){return s.size() >= 5;}void show(const std::string &s){std::cout << s << std::endl;}int main(){using namespace std;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete" };auto tmp = partition(vstr.begin(), vstr.end(), isShorter);//把一元谓词为真的值放在左边for_each(vstr.begin(), tmp, show);system("pause");return 0;}

10.14

[](int n,int m){return n+m;}

10.15

[n](int m){reurn n+m;}

10.16

#include <iostream>#include <vector>#include <algorithm>//sort unique stable_sort find_if for_each#include <string>void elimDups(std::vector<std::string> &vstr){sort(vstr.begin(), vstr.end());//默认排序auto u_end = unique(vstr.begin(), vstr.end());//删除连续相同的元素vstr.erase(u_end, vstr.end());//清理空元素}void biggies(std::vector<std::string> &s, std::vector<std::string>::size_type sz){elimDups(s);stable_sort(s.begin(), s.end(), [](const std::string &s1, const std::string &s2){return s1.size() < s2.size(); });//长度相同的单词按二元谓词排序auto wc = find_if(s.begin(), s.end(), [sz](const std::string &s){return s.size() >= sz; });//记录第一次大小大于sz的位置auto count = s.end() - wc;//统计元素尾到wc的位置的距离std::cout << count << " " << (sz ? "word" : "s") << " of length " << sz << " or longer" << std::endl;for_each(wc, s.end(), [](const std::string &s){std::cout << s << "\t"; });std::cout << std::endl;}int main(){using namespace std;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete" };elimDups(vstr);for (auto s : vstr)cout << s << endl;system("pause");return 0;}

10.17

#include "../../7.21/7.21/标头.h"#include <vector>#include <algorithm>//sortint main(){using namespace std;vector<Sales_data> vsd;Sales_data temp;while (read(cin, temp))vsd.push_back(temp);sort(vsd.begin(), vsd.end(), [](Sales_data &s1, Sales_data &s2){return s1.isbn().size() < s2.isbn().size(); });for (auto &x : vsd)cout << x.isbn() << endl;system("pause");return 0;}

10.18

#include <iostream>#include <vector>#include <algorithm>//sort unique stable_sort partition for_each#include <string>void elimDups(std::vector<std::string> &vstr){sort(vstr.begin(), vstr.end());auto u_end = unique(vstr.begin(), vstr.end());vstr.erase(u_end, vstr.end());}void biggies(std::vector<std::string> &s, std::vector<std::string>::size_type sz){elimDups(s);stable_sort(s.begin(), s.end(), [](const std::string &s1, const std::string &s2){return s1.size() < s2.size(); });auto wc = partition(s.begin(), s.end(), [sz](const std::string &s){return s.size() >= sz; });//把一元谓词条件为真的元素排序到左边，并返回最后一个条件为真的迭代器auto count = s.end() - wc;std::cout << count << " " << (sz ? "word" : "s") << " of length " << sz << " or longer" << std::endl;for_each(wc, s.end(), [](const std::string &s){std::cout << s << "\t"; });std::cout << std::endl;}int main(){using namespace std;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete" };elimDups(vstr);for (auto s : vstr)cout << s << endl;system("pause");return 0;}

10.19

#include <iostream>#include <vector>#include <algorithm>#include <string>void elimDups(std::vector<std::string> &vstr){sort(vstr.begin(), vstr.end());auto u_end = unique(vstr.begin(), vstr.end());vstr.erase(u_end, vstr.end());}void biggies(std::vector<std::string> &s, std::vector<std::string>::size_type sz){elimDups(s);stable_sort(s.begin(), s.end(), [](const std::string &s1, const std::string &s2){return s1.size() < s2.size(); });auto wc=stable_partition(s.begin(), s.end(), [sz](const std::string &s){return s.size() < sz; });auto count = s.end() - wc;std::cout << count << " " << (sz ? "word" : "s") << " of length " << sz << " or longer" << std::endl;for_each(wc, s.end(), [](const std::string &s){std::cout << s << "\t"; });std::cout << std::endl;}int main(){using namespace std;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete" };biggies(vstr, 5);system("pause");return 0;}

10.20

#include <iostream>#include <string>#include <vector>#include <algorithm>//count_ifint main(){using namespace std;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete" };int count = count_if(vstr.begin(), vstr.end(), [](const string &s)->bool{return s.size() >= 6 ? true : false; });//接受一个一元谓词，统计谓词为真的次数cout << count << endl;system("pause");return 0;}

10.21

auto fun=[&n](){return n?true:false;}while(fun())//

10.22

#include <iostream>#include <vector>#include <string>#include <functional>//bind#include <algorithm>//conut_ifbool isfun(const std::string &s, std::string::size_type n){return s.size() <= n;}int main(){using namespace std;using namespace std::placeholders;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete" };cout << count_if(vstr.cbegin(), vstr.cend(), bind(isfun, _1, 6));//bind返回一个一元谓词，并把6绑定为isfun的第二个参数system("pause");return 0;}

10.23

1+n个，至少一个谓词

10.24

#include <iostream>#include <string>#include <vector>#include <functional>//bind#include <algorithm>//find_ifbool check_size(std::string::size_type n,const std::string &s){return s.size() < n;}int main(){using namespace std;using namespace std::placeholders;string str = "666666";vector<int> vi{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };cout << *find_if(vi.begin(), vi.end(), bind(check_size, _1, str)); //返回一个一元谓词，str绑定check_size的stringsystem("pause");return 0;}

10.25

#include <iostream>#include <vector>#include <algorithm>#include <string>#include <functional>//bindvoid elimDups(std::vector<std::string> &vstr){sort(vstr.begin(), vstr.end());auto u_end = unique(vstr.begin(), vstr.end());//消除重复vstr.erase(u_end, vstr.end());//清空消除重复后留下的空余}bool check_size(const std::string &s, std::string::size_type n){return s.size() > n;}void biggies(std::vector<std::string> &s, std::vector<std::string>::size_type sz){elimDups(s);//排序，消除重复stable_sort(s.begin(), s.end(), [](const std::string &s1, const std::string &s2){return s1.size() < s2.size(); });//在大小相等的情况下排序partition(s.begin(), s.end(), bind(check_size,std::placeholders::_1,sz));//再次排序，把大的放左边bind返回一元谓词，sz绑定第二个参数for_each(s.begin(), s.end(), [](const std::string &s){std::cout << s << "\t"; });//输出}int main(){using namespace std;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete","the","minecaft","microsoft" };biggies(vstr, 5);for (auto s : vstr)cout << s << endl;system("pause");return 0;}

10.26

iter=back_inserter(vec)返回一个push_back的迭代器

当使用其赋值时相当于调用push_back将元素添加到末尾:iter=9; //相当于vec.push_back(9);需要容器支持push_back

iter=front_inserter(lst)返回一个push_front的迭代器

当使用其赋值时相当于调用push_front将元素添加到首:iter=0; //相当于lst.push_front(0);需要容器支持push_front

iter=inserter(lst,it)返回一个指向lst容器一个位置的迭代器

当使用其赋值时相当于调用inserter(it,val)将元素添加到it指定的位置之前:iter=1; //相当于lst.inserter(it,1);需要容器支持inserter

10.27

#include <iostream>#include <vector>#include <string>#include <algorithm>int main(){using namespace std;vector<string> vstr = { "c++", "false", "string", "delete", "c++", "string", "visual", "studio", "c++", "basic", "true", "system", "delete" };vector<string> vstr2;sort(vstr.begin(), vstr.end());unique_copy(vstr.begin(), vstr.end(), std::back_inserter(vstr2));for_each(vstr2.begin(), vstr2.end(), [](const string &s){cout << s << endl; });system("pause");return 0;}

10.28

#include <iostream>#include <vector>#include <list>#include <iterator>//inserater、back_inserater、front_inserterint main(){using namespace std;vector<int> vi{ 1, 2, 3, 4, 5, 6, 7, 8, 9 };list<int> vi1, vi2, vi3;//不用vector是因为没有push_frontcopy(vi.begin(), vi.end(), inserter(vi1, vi1.begin()));//将元素从首开始添加copy(vi.begin(), vi.end(), back_inserter(vi2));//将元素添加到尾copy(vi.begin(), vi.end(), front_inserter(vi3));/将元素添加到头for (auto &x : vi1)cout << x << "\t";cout << endl;for (auto &x : vi2)cout << x << "\t";cout << endl;for (auto &x : vi3)cout << x << "\t";cout << endl;system("pause");return 0;}

10.29

#include <iostream>#include <vector>#include <fstream>#include <iterator>//back_inserter#include <string>#include <algorithm>//copyint main(int argc, char **argv){using namespace std;ifstream ifile(argv[1]);if (!ifile){cerr << "open file error!";exit(1);}istream_iterator<string> ifstr(ifile), eof;//把流绑定到文件流vector<string> vstr;copy(ifstr, eof, back_inserter(vstr));copy(vstr.begin(), vstr.end(), ostream_iterator<string>(cout, "\n"));//从vstr读取数据并赋值到标准输出流迭代器，格式为 数据+"\n"ifile.close();return 0;}

10.30

#include <iostream>#include <algorithm>//sort#include <vector>#include <iterator>//istream_iterator、ostream_iteratorusing namespace std;int main(){istream_iterator<int> itint(cin),eof;ostream_iterator<int> otint(cout);vector<int> vi;while (itint != eof)//or copy(itint,eof,back_insertor(vi));vi.push_back(*itint++);sort(vi.begin(), vi.end());copy(vi.begin(), vi.end(), otint);system("pause");return 0;}

10.31

#include <iostream>#include <algorithm><span style="white-space:pre"></span>//copy<span style="white-space:pre"></span>sort<span style="white-space:pre"></span>unique_copy#include <vector>#include <iterator>int main(){<span style="white-space:pre"></span>using namespace std;<span style="white-space:pre"></span>istream_iterator<int> itint(cin), eof;<span style="white-space:pre"></span>vector<int> vi;<span style="white-space:pre"></span>copy(itint, eof, back_inserter(vi));<span style="white-space:pre"></span>sort(vi.begin(), vi.end());<span style="white-space:pre"></span>unique_copy(vi.begin(), vi.end(), ostream_iterator<int>(cout,"\t"));<span style="white-space:pre"></span>system("pause");<span style="white-space:pre"></span>return 0;}

10.32

#include "Sales_item.h"#include <iostream>#include <vector>#include <algorithm>#include <iterator>#include <numeric>//accumulateint main(){using namespace std;istream_iterator<Sales_item> sit(std::cin),eof;vector<Sales_item> vs;copy(sit, eof, back_inserter(vs));sort(vs.begin(), vs.end(), [](const Sales_item &s1, const Sales_item &s2){return s1.isbn < s2.isbn; });for (auto beg = vs.begin(), tmp = beg; beg != vs.end(); beg = tmp)//beg和tmp用于记录相同的元素的范围{tmp = find_if(beg, vs.end(), [beg](const Sales_item &s){return s.isbn != beg->isbn; });//找到范围，（beg，tmp]之间的元素同名的(isbn值）accumulate(beg, tmp, Sales_item(beg->isbn));//初始值为0的Sales_item对象}for (auto &x : vs)cout << x << endl;system("pause");return 0;}

10.33

#include <iostream>#include <fstream>#include <iterator>//istream_iterator、ostream_iterator#include <algorithm>//for_eachint main(int argc, char **argv){using namespace std;ifstream ifile(argv[1]);if (!ifile){cerr << "open file error!";exit(1);}ofstream of1(argv[2]),of2(argv[3]);if ((!of1)&&(!of2)){cerr << "open file error!1";exit(2);}istream_iterator<int> itf(ifile), eof;ostream_iterator<int> otf1(of1," "),otf2(of2,"\n");for_each(itf, eof, [&otf1, &otf2](int i){*(i % 2 ? otf1 : otf2)++ = i; });//相当于：/*int t;while (itf != eof){if ((t = *itf++) % 2)*otf1++ = t;else*otf2++ = t;}*/system("pause");return 0;}

10.34

#include <iostream>#include <vector>int main(){using namespace std;vector<int> vec{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };for (auto beg = vec.crbegin(); beg != vec.crend(); ++beg)//crebgin返回尾迭代器crend返回首前迭代器cout << *beg;system("pause");return 0;}

10.35

#include <iostream>#include <vector>int main(){using namespace std;vector<int> vec{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };for (auto beg = vec.cbegin(); beg != vec.cend(); ++beg)cout << *beg;system("pause");return 0;}

10.36

#include <iostream>#include <list>int main(){using namespace std;list<int> li{ 1, 0, 6, 3, 5, 5, 2, 3, 0, 8, 1, 0, 5 };cout << *find(li.rbegin(), li.rend(), 0);system("pause");return 0;}

10.37

#include <iostream>#include <vector>#include <list>int main(){using namespace std;vector<int> vi{ 1,2,3,4,5,6,7,8,9};list<int> li(vi.crbegin() + 2, vi.crend() - 2);//(3,7]/*list<int> li;copy(vi.crbegin() + 2, vi.crbegin() + 7, back_inserter(li));*/for (auto x : li)cout << x << "\t";system("pause");return 0;}

10.38

                  input iterator:==、!=、++、等号右边*n、->

                output iterator:++,等号左边*n

              forward iterator:==、!=、++、*n、->

             bidirectional iterator:==、!=、++、*n、->、--

        random-access iterator:==, !=、 <、<=、 >、>=、++、--、+、+=、-、-=、-(两个迭代器)、*、->、iter[n] == * (iter + n)

10.39

list属于bidirectional、vector属于random-access

10.40

copy需要一对输入迭代器和一个输出迭代器

reverse需要一对方向迭代器

unique需要一对向前迭代器

10.41

迭代器beg到end中的old_val替换为new_val

迭代器beg到end中谓词pred为真的替换为new_val

迭代器beg到end中出现old_val时，添加new_val到dest

迭代器beg到end中谓词pred为真时，添加new_val到dest

10.42

#include <iostream>#include <list>#include <string>void elimDups(std::list<std::string> &vstr){vstr.sort();vstr.unique();}int main(){using namespace std;list<string> vstr = { "111", "222", "333", "444", "222", "333", "555", "777", "111", "888", "666", "666", "999" };elimDups(vstr);for (auto s : vstr)cout << s << endl;system("pause");return 0;}