C++Primer第五版 第十章 泛型算法

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10.1 概述

1 泛型算法：实现了一些经典算法的公共接口，如排序和搜索，可以用于不同类型的元素和多种容器类型

2 基本上都定义在algorithm和numeric两个头文件中

3 迭代器令算法不依赖于容器，依赖于元素类型的操作

练习10.1

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

using namespace std;

int main() {
	int t, n;
	vector<int> vec;
	cout << "请输入int序列个数：" << endl;
	cin >> n;
	cout << "请输入int序列：" << endl;
	for (int i = 0;i < n;i++) {
		cin >> t;
		vec.push_back(t);
	}
	cout << "请输入要统计的值：" << endl;
	int num;
	cin >> num;
	cout << count(vec.begin(), vec.end(), num) << endl;
	
	system("pause");
	return 0;
}

练习10.2

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

using namespace std;

int main() {
	int num = 0,t = 0;
	string s1;
	list <string> lst;
	cout << "请输入字符串序列数量" << endl;
	cin >> t;
	cout << "请输入" << t << "个字符串" << endl;
	for (int i = 0; i < t; i++){
		cin >> s1;
		lst.push_back(s1);
	}
	cout << "请输入要统计的字符串：" << endl;
	string s2;
	cin >> s2;
	cout << count(lst.begin(), lst.end(), s2) << endl;

	system("pause");
	return 0;
}

10.2 初识泛型算法

1 标准库基本上都是对一个范围内的容器进行操作，所以参数中总会有两个表示范围的迭代器

2 对于读取而不改变元素的算法，最好使用cbegin()和cend(),否则用begin()和end()

练习10.3

#include<iostream>
#include<numeric>
#include<vector>

using namespace std;

int main() {
	vector<int> vec = { 1,2,3 };
	int sum = accumulate(vec.cbegin(), vec.cend(), 0);
	cout << sum << endl;
	return 0;
}

练习10.4

将初值设定为0，表明返回值为int类型，使用之后，会将double转换为int，损失精度

练习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。

练习10.6

fill_n(vec.begin(),vec.size(),0);//注意其三个参数的意义

练习10.7

(a)：lst和vec之间的大小未保证相同，vec.resize(lst.size)

(b)：reverse是改变容器容量的，并没有改变其大小，用resize()

练习10.8

算法只是产生了一个插入迭代器，然后使用这个迭代器进行插入操作。

练习10.9

#include<iostream>
#include<numeric>
#include<vector>
#include<algorithm>
#include<string>
using namespace std;

void elimDups(vector<string> &words) {
	sort(words.begin(), words.end());
	auto end_unique = unique(words.begin(), words.end());
	cout << "unique后：";
	for (auto i : words) {
		cout << i << " ";
	}
	cout << endl;
	cout << "erase后：";
	words.erase(end_unique, words.end());
	for (auto i : words) {
		cout << i << " ";
	}
	cout << endl;
}

int main() {
	vector<string> words = { "I", "love", "you", "I", "love", "you", "I" };
	elimDups(words);
	system("pause");
	return 0;
}

练习10.10

算法只作用于迭代器，而不直接对容器进行操作。

练习10.11

#include<iostream>
#include<numeric>
#include<vector>
#include<algorithm>
#include<string>
using namespace std;

void elimDups(vector<string> &words) {
	cout << "isShorter后：";
	stable_sort(words.begin(), words.end(),isShorter);
	auto end_unique = unique(words.begin(), words.end());
	cout << "unique后：";
	for (auto i : words) {
		cout << i << " ";
	}
	cout << endl;
	cout << "erase后：";
	words.erase(end_unique, words.end());
	for (auto i : words) {
		cout << i << " ";
	}
	cout << endl;
}

int main() {
	vector<string> words = { "I", "love", "you", "I", "love", "you", "I" };
	elimDups(words);
	system("pause");
	return 0;
}

练习10.12

bool compareIsbn(const Sales_data &a, const Sales_data &b) {
        return a.isbn() < b.isbn();
}

练习10.13

#include<iostream>
#include<numeric>
#include<vector>
#include<algorithm>
#include<string>
using namespace std;

bool cmp(const string &a) {
	return a.size() >= 5;
}

int main() {
	vector<string> words = { "the","quick","red","fox","jumps","over","the","slow","red","turtle" };
	partition(words.begin(), words.end(), cmp);
	for (auto &i : words) {
		cout << i << " ";
	}
	cout << endl;
	system("pause");
	return 0;
}

练习10.14

#include<iostream>
using namespace std;
int main() {
	auto f = [](int a,int b) {return a + b;};
	cout << f(1, 2) << endl;
	return 0;
}

练习10.15

#include<iostream>
using namespace std;

int main() {
	int a = 1;
	auto f = [a](int b) {return a + b;};
	cout << f(2) << endl;
	
	system("pause");
	return 0;
}

练习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 = { "the","quick","red","fox","jumps","over","the","slow","red","turtle" };

	biggies(vs, 5);

	return 0;
}

练习10.17

#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<numeric>
using namespace std;
 
class Sales_data
{
public:
	Sales_data();
	Sales_data(string s):_isbn(s)//列表初始化格式（：类内变量名（初始化值），）
	{
 
	}
	string isbn()
	{
		return _isbn;
	}
	string _isbn;
};
 
int main(int argc, char**argv)
{
	Sales_data a("because");//初始化对象
	Sales_data b("I");
	Sales_data c("Like");
	Sales_data d("your");
	Sales_data e("beautiful");
	Sales_data f("eyes");
 
	vector<Sales_data> vec1;//VS2010不支持列表初始化
	vec1[0] = a;
	vec1[1] = b;
	vec1[2] = c;
	vec1[3] = d;
	vec1[4] = e;
	vec1[5] = f;
 
	stable_sort(vec1.begin(),vec1.end(),[](Sales_data s1, Sales_data s2){return s1.isbn().size() < s2.isbn().size();});//排序
	cout<<"排序后的vector:";
	for(int i = 0; i < vec1.size(); ++i)
	{
		cout<<vec1[i].isbn()<<" ";
	}
 
	return 0;
}

练习10.18-19

#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);
	auto wc = partition(words.begin(), words.end(),
		[sz](const string &a)
	{ return a.size() >= sz; });
    
//auto wc = stable_partition(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 = { "the","quick","red","fox","jumps","over","the","slow","red","turtle" };

	biggies(vs, 5);
	system("pause");
	return 0;
}

练习10.20

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

using namespace std;

int main()
{
	vector<string> words = { "the","quick","red","fox","jumps","over","the","slow","red","turtle" };
	string::size_type sz = 6;
	auto wc = count_if(words.begin(), words.end(),
		[sz](const string &a)
	{ return a.size() >= sz; });
	cout << wc << endl;
	system("pause");
	return 0;
}

练习10.21

#include<iostream>
#include<algorithm>

using namespace std;

int main() {
	int v = 5;
	auto f = [&v]()->bool
	{
		if (v <= 0) return false;
		else {
			--v;
			return true;
		}
	};
	while (f()) {
		cout << v << endl;
	}
	system("pause");
	return 0;
}