C++Primer第五版 习题答案 第十章 泛型算法（Generic Algorithms）

其他 2018-10-10 19:41:02 阅读次数: 0

10.1

#include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

int main()
{
	vector<int> v1 = {1,2,3,1,1};

	cout << count(v1.cbegin(), v1.cend(), 1) << endl;

	return 0;
}

10.2

#include <list>
#include <iostream>
#include <algorithm>
#include <string>

using namespace std;

int main()
{
	list<string> l1 = {"a", "b", "c", "a", "aa"};

	cout << count(l1.cbegin(), l1.cend(), "a") << endl;

	return 0;
}

10.3

#include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

int main()
{
	vector<int> v1 = {1,2,3,1,1};

	cout << accumulate(v1.cbegin(), v1.cend(), 0) << endl;

	return 0;
}

10.4

结果默认是int类型的，精度会降低。

#include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

int main()
{
	vector<double> v1 = {1,2,3.1,1,1};

	cout << accumulate(v1.cbegin(), v1.cend(), 0) << endl;

	return 0;
}

10.5

equal会比较指针地址，而不是字符串值，比较的结果与string类型的不一致。

10.6

#include <iostream>
#include <vector>
#include <iterator>

using namespace std;

int main()
{
	vector<int> v1(10, 1);
	fill_n(v1.begin(), v1.size(), 0);
	for(const auto i : v1)
		cout << i << " ";
	cout << endl;

	vector<int> v2;
	fill_n(back_inserter(v2), 10, 0);
	for(const auto i : v2)
		cout << i << " ";
	cout << endl;

	return 0;
}

10.7

（a）10.4.1中说明back_inserter(vec)

copy(lst.cbegin(), lst.cend(), back_inserter(vec));

（b）没有报错，但是与预期不符，vec并没有10个元素，且每个元素都为0。可以加上

vec.resize(10);

或改为：

fill_n(back_inserter(v), 10, 0);

10.8

back_inserter是的一部分，而不是。

10.9

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> &elimDups(vector<string> &words)
{
	sort(words.begin(), words.end());
	auto end_unique = unique(words.begin(), words.end());
	words.erase(end_unique, words.end());
	return words;
}

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e"};

	for(const auto s : elimDups(vs))
		cout << s << " ";
	cout << endl;

	return 0;
}

10.10

改变容器大小可能会导致迭代器失效，而且每种容器都有自己的特性，改变容器大小可能需要使用不同的方法，不改变容器大小使得算法更加通用。

10.11

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> &elimDups(vector<string> &words)
{
	sort(words.begin(), words.end());
	auto end_unique = unique(words.begin(), words.end());
	words.erase(end_unique, words.end());
	return words;
}

bool isShorter(const string &s1, const string &s2)
{
	return s1.size() < s2.size();
}

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e","bb","aa","aaa"};

	for(const auto s : elimDups(vs))
		cout << s << " ";
	cout << endl;

	stable_sort(vs.begin(), vs.end(), isShorter);

	for(const auto s : vs)
		cout << s << " ";
	cout << endl;

	return 0;
}

10.12

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include "../ch07_Classes/Sales_data_ex26.h"
#include <sstream>
#include <fstream>
#include <iostream>

using namespace std;

bool compareIsbn(const Sales_data &sales_data1, const Sales_data &sales_data2)
{
	return sales_data1.isbn() < sales_data2.isbn();
}

int main()
{
	vector<string> v1;

	ifstream is("../ch08_The_IO_Library/book_sales");
	string buf;

	if(!is)
	{
		cerr << "open error" << endl;
		return -1;
	}

	while(getline(is, buf))
		v1.push_back(buf);

	vector<Sales_data> v2;
	for(const auto &s : v1)
	{
		// cout << s << endl;
		istringstream iss(s);
		v2.push_back(Sales_data(iss));
	}

	stable_sort(v2.begin(), v2.end(), compareIsbn);

	for(const auto s : v2)
		cout << s.isbn() << endl;

	return 0;
}

10.13

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> &elimDups(vector<string> &words)
{
	sort(words.begin(), words.end());
	auto end_unique = unique(words.begin(), words.end());
	words.erase(end_unique, words.end());
	return words;
}

bool greater_than_5(const string &s)
{
	return s.size() >= 5;
}

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e","bb","aa","aaa","aaaaa"};

	auto iter = partition(vs.begin(), vs.end(), greater_than_5);
	for(const auto s : vs)
		cout << s << " ";
	cout << endl;

	vs.erase(iter, vs.end());
	for(const auto s : vs)
		cout << s << " ";
	cout << endl;

	return 0;
}

10.14

#include <iostream>

using namespace std;

int main()
{
	auto add_int = [](int x, int y){return x + y;};
	cout << add_int(1, 2) << endl;
	
	return 0;
}

10.15

#include <iostream>

using namespace std;

int main()
{
	int x = 1;
	auto add_int = [x](int y){return x + y;};

	cout << add_int(2) << endl;
	
	return 0;
}

10.16

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> &elimDups(vector<string> &words)
{
	sort(words.begin(), words.end());
	auto end_unique = unique(words.begin(), words.end());
	words.erase(end_unique, words.end());
	return words;
}

void biggies(vector<string> &words, vector<string>::size_type sz)
{
	elimDups(words);
	stable_sort(words.begin(), words.end(),
		[](const string &a, const string &b)
			{ return a.size() < b.size(); });
	auto wc = find_if(words.begin(), words.end(),
		[sz](const string &a)
			{ return a.size() >= sz; });
	auto count = words.end() - wc;
	cout << count << endl;
	for(const auto s : words)
		cout << s << " ";
	cout << endl;
}

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e","bb","aa","aaa","aaaaa"};

	biggies(vs, 5);

	return 0;
}

10.17

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include "../ch07_Classes/Sales_data_ex26.h"
#include <sstream>
#include <fstream>
#include <iostream>

using namespace std;

int main()
{
	vector<string> v1;

	ifstream is("../ch08_The_IO_Library/book_sales");
	string buf;

	if(!is)
	{
		cerr << "open error" << endl;
		return -1;
	}

	while(getline(is, buf))
		v1.push_back(buf);

	vector<Sales_data> v2;
	for(const auto &s : v1)
	{
		// cout << s << endl;
		istringstream iss(s);
		v2.push_back(Sales_data(iss));
	}

	stable_sort(v2.begin(), v2.end(), []
		(const Sales_data &sales_data1, const Sales_data &sales_data2)
			{ return sales_data1.isbn() < sales_data2.isbn(); });

	for(const auto s : v2)
		cout << s.isbn() << endl;

	return 0;
}

10.18

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> &elimDups(vector<string> &words)
{
	sort(words.begin(), words.end());
	auto end_unique = unique(words.begin(), words.end());
	words.erase(end_unique, words.end());
	return words;
}

void biggies(vector<string> &words, vector<string>::size_type sz)
{
	elimDups(words);
	stable_sort(words.begin(), words.end(),
		[](const string &a, const string &b)
			{ return a.size() < b.size(); });
	auto wc = partition(words.begin(), words.end(),
		[sz](const string &a)
			{ return a.size() >= sz; });
	auto count = wc - words.begin();
	cout << count << endl;
	for(const auto s : words)
		cout << s << " ";
	cout << endl;
}

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e","bb","aa","aaa","aaaaa"};

	biggies(vs, 5);

	return 0;
}

10.19

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> &elimDups(vector<string> &words)
{
	sort(words.begin(), words.end());
	auto end_unique = unique(words.begin(), words.end());
	words.erase(end_unique, words.end());
	return words;
}

void biggies(vector<string> &words, vector<string>::size_type sz)
{
	elimDups(words);
	stable_sort(words.begin(), words.end(),
		[](const string &a, const string &b)
			{ return a.size() < b.size(); });
	auto wc = partition(words.begin(), words.end(),
		[sz](const string &a)
			{ return a.size() >= sz; });
	auto count = wc - words.begin();
	cout << count << endl;
	for(const auto s : words)
		cout << s << " ";
	cout << endl;
}

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e","bb","aa","aaa","aaaaa"};

	biggies(vs, 5);

	return 0;
}

10.20

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e","bb","aa","aaa","aaaaa"};
	string::size_type sz = 6;

	cout << count_if(vs.begin(), vs.end(),
		[sz](const string &s)
			{ return s.size() >=sz; }) << endl;

	return 0;
}

10.21

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
	int i = 6;

	auto reduce_i = [&i]() -> bool 
	{
		if(i <= 0)
			return false;
		else
		{
			--i;
			return true;
		}
	};

	while(reduce_i())
	{
		cout << i << endl;
	}

	return 0;
}

10.22

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;
bool judge_size(string &s, string::size_type sz)
{
	return s.size() >= sz;
}

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e","bb","aa","aaa","aaaaa"};

	cout << count_if(vs.begin(), vs.end(), bind(judge_size, placeholders::_1, 6)) << endl;

	return 0;
}

10.23

假设要绑定的函数有n个参数，绑定取n + 1个参数。另外一个是函数本身的绑定。

10.24

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;
bool check_size(string &s, int sz)
{
	return s.size() < sz;
}

int main()
{
	vector<int> vi = {1,2,3,4,5,6};
	string s("aaaa");

	auto iter = find_if(vi.begin(), vi.end(), bind(check_size, s, placeholders::_1));

	cout << *iter << endl;

	return 0;
}

10.25

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> &elimDups(vector<string> &words)
{
	sort(words.begin(), words.end());
	auto end_unique = unique(words.begin(), words.end());
	words.erase(end_unique, words.end());
	return words;
}

bool check_size(const string &s, string::size_type sz)
{
	return s.size() >= sz;
}

int main()
{
	vector<string> vs = {"d","c","b","a","a","c","e","bb","aa","aaa","aaaaa"};

	auto iter = partition(vs.begin(), vs.end(), bind(check_size, placeholders::_1, 5));
	for(const auto s : vs)
		cout << s << " ";
	cout << endl;

	vs.erase(iter, vs.end());
	for(const auto s : vs)
		cout << s << " ";
	cout << endl;

	return 0;
}

10.26

back_inserter创建一个使用push_back的迭代器；
front_inserter创建一个使用push+front的迭代器；
inserter创建一个使用insert的迭代器。此函数接受第二个参数，这个参数必须是一个指向给定容器的迭代器。元素将被插入到给定迭代器所表示的元素之前。

10.27

#include <iostream>
#include <vector>
#include <list>
#include <algorithm>

using namespace std;

int main()
{
	vector<int> v1 = {1,1,1,2,3,4,5};
	list<int> l1;

	unique_copy(v1.begin(),v1.end(),back_inserter(l1));

	for(const auto i : l1)
		cout << i << " ";
	cout << endl;

	return 0;
}

10.28

#include <iostream>
#include <vector>
#include <list>
#include <algorithm>

using namespace std;

int main()
{
	vector<int> v1 = {1,2,3,4,5,6,7,8,9};
	list<int> l1,l2,l3;

	copy(v1.begin(),v1.end(),back_inserter(l1));
	for(const auto i : l1)
		cout << i << " ";
	cout << endl;

	copy(v1.begin(),v1.end(),front_inserter(l2));
	for(const auto i : l2)
		cout << i << " ";
	cout << endl;

	copy(v1.begin(),v1.end(),inserter(l3,l3.begin()));
	for(const auto i : l3)
		cout << i << " ";
	cout << endl;

	return 0;
}

10.29

#include <iostream>
#include <iterator>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
	ifstream ifs("../ch08_The_IO_Library/data");
	istream_iterator<string> str_istream_iter(ifs), eof;
	vector<string> v1(str_istream_iter, eof);
	ostream_iterator<string> cout_iter(cout, " ");
	copy(v1.begin(), v1.end(), cout_iter);
	cout << endl;

	return 0;
}

10.30

#include <iostream>
#include <iterator>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
	istream_iterator<int> int_cin(cin), eof;
	vector<int> v1(int_cin, eof);
	sort(v1.begin(), v1.end());
	ostream_iterator<int> cout_iter(cout, " ");
	copy(v1.begin(), v1.end(), cout_iter);
	cout << endl;

	return 0;
}

10.31

#include <iostream>
#include <iterator>
#include <vector>
#include <algorithm>
#include "../ch01_Getting_Started/Sales_item.h"

using namespace std;

int main()
{
	istream_iterator<Sales_item> int_cin(cin), eof;
	vector<Sales_item> v1(int_cin, eof);
	sort(v1.begin(), v1.end(), compareIsbn);
	// for(const auto s : v1)
	// 	cout << s.isbn() << endl;
	cout << endl;
	for(auto beg = v1.cbegin(), end = beg; beg != v1.cend(); beg = end)
	{
		end = find_if(beg, v1.cend(), [beg](const Sales_item &sale_item){ return sale_item.isbn() != beg->isbn(); });
		cout << accumulate(beg, end, Sales_item(beg->isbn())) << endl;
	}

	return 0;
}

10.32

之前谓词处写了sale_item != *beg，找了半天才发现这是检查3个成员变量的。

#include <iostream>
#include <iterator>
#include <fstream>
#include <vector>
#include <algorithm>
#include "../ch01_Getting_Started/Sales_item.h"

using namespace std;

int main()
{
	istream_iterator<Sales_item> int_cin(cin), eof;
	vector<Sales_item> v1(int_cin, eof);
	sort(v1.begin(), v1.end(), compareIsbn);
	// for(const auto s : v1)
	// 	cout << s.isbn() << endl;
	cout << endl;
	for(auto beg = v1.cbegin(), end = beg; beg != v1.cend(); beg = end)
	{
		end = find_if(beg, v1.cend(), [beg](const Sales_item &sale_item){ return sale_item.isbn() != beg->isbn(); });
		cout << accumulate(beg, end, Sales_item(beg->isbn())) << endl;
	}

	return 0;
}

10.33

#include <iostream>
#include <iterator>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

int main(int argc, char **argv)
{
	if(argc != 4) return -1;

	ifstream ifs(argv[1]);
	istream_iterator<int> int_istream_iter(ifs), eof;
	vector<int> v1(int_istream_iter, eof);
	
	ofstream ofs_odd("argv[2]");
	ostream_iterator<int> odd_iter(ofs_odd, "\n");
	copy_if(v1.begin(), v1.end(), odd_iter, [](int i){return i % 2; });
	ofs_odd.close();

	ofstream ofs_even("argv[3]");
	ostream_iterator<int> even_iter(ofs_even, "\n");
	copy_if(v1.begin(), v1.end(), even_iter, [](int i){return !(i % 2); });
	ofs_even.close();

	return 0;
}

10.34

#include <iostream>
#include <iterator>
#include <vector>

using namespace std;

int main()
{
	vector<int> v1 = {1,2,3,4,5,6,7,8};

	for(auto r_iter = v1.crbegin(); r_iter != v1.crend(); ++r_iter)
		cout << *r_iter << " ";
	cout << endl;

	return 0;
}

10.35

#include <iostream>
#include <iterator>
#include <vector>

using namespace std;

int main()
{
	vector<int> v1 = {1,2,3,4,5,6,7,8};

	for(auto iter = v1.end()-1; iter != v1.begin()-1; --iter)
		cout << *iter << " ";
	cout << endl;

	return 0;
}

10.36

#include <iostream>
#include <iterator>
#include <list>
#include <algorithm>

using namespace std;

int main()
{
	list<int> l1 = {1,2,3,4,5,6,7,8,0};

	// for(auto r_iter = l1.crbegin(); r_iter != l1.crend(); ++r_iter)
	// 	cout << *r_iter << " ";
	// cout << endl;

	auto r_iter = find(l1.crbegin(), l1.crend(), 0);
	// r_iter.base();
	cout << distance(r_iter, l1.crend()) << endl;
	// cout << l1.end() - l1.begin() << endl;

	return 0;
}

10.37

#include <iostream>
#include <iterator>
#include <vector>
#include <list>
#include <algorithm>

using namespace std;

int main()
{
	vector<int> v1 = {1,2,3,4,5,6,7,8,9,0};
	list<int> l1(v1.crbegin()+2,v1.crbegin()+7);

	for(const auto i : l1)
		cout << i << " ";
	cout << endl;

	return 0;
}

10.38

输入迭代器：、!=、++、、->；
输出迭代器：++、；
前项迭代器：、!=、++、、->；
双向迭代器：==、!=、++、–、、->；
随机访问迭代器：==、!=、++、–、、->、<、<=、>、>=、+、+=、-、-=、-、iter[n]、(iter[n])。

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10.39

list术语双向迭代器；vector属于随机访问迭代器。

10.40

copy：前两个参数为输入迭代器，第三个参数为输出迭代器；
reverse：双向迭代器；
unique：前向迭代器。

10.41

replace(beg, end, old_val, new_val); // 在beg与end之间，如果是old_val则替换为new_val
replace_if(beg, end, pred, new_val); // 在beg与end之间，如果满足谓词条件则替换为new_val
replace_copy(beg, end, dest, old_val, new_val); // 在beg与end之间，如果是old_val则替换为new_val，不改变原始值，将结果复制到dest
replace_copy_if(beg, end, dest, pred, new_val); // 在beg与end之间，如果满足谓词条件则替换为new_val，不改变原始值，将结果复制到dest

10.42

#include <iostream>
#include <string>
#include <list>
#include <algorithm>

using namespace std;

list<string> &elimDups(list<string> &words)
{
	// sort(words.begin(), words.end());
	words.sort();
	words.unique();
	// auto end_unique = unique(words.begin(), words.end());
	// words.erase(end_unique, words.end());
	return words;
}

int main()
{
	list<string> vs = {"d","c","b","a","a","c","e"};

	for(const auto s : elimDups(vs))
		cout << s << " ";
	cout << endl;

	return 0;
}

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