C++ 的常见算法之三

合并
- merge
- - 使用实列
- inplace_merge
- - 使用实列
- set_difference
- - 使用实列
堆
- make_heap
- - 使用实列
- sort_heap
- - 使用实列

合并

merge

将排序范围 [first1,last1) 和 [first2,last2) 中的元素合并到一个新范围中，该范围从 result 开始，所有元素均已排序。

第一个版本使用operator< 来比较元素，
第二个版本使用comp 来比较元素。两个范围中的元素应已根据相同的标准（operator< 或 comp）进行排序。结果范围也按此排序。

使用实列

#include <iostream> 
#include <algorithm>
#include <vector>using namespace std;struct personnel {string  name;int     age;
};void print_element(int val) { cout << val << " " ; }
void print_personnel(personnel person) { cout << person.name << " " << person.age << endl; }struct sort_class {bool operator() (personnel lf, personnel lr) { return (lf.age < lr.age);}
} sort_object;int main () {int first[] = {5,10,15,20,25};int second[] = {50,40,30,20,10};vector<int> v(10);vector<personnel> it_depart = {{"John", 30},{"Allison", 25},		  {"Sam", 29},		  {"Alice", 39},		  };vector<personnel> hr_depart = {{"Michael", 40},{"Tommy", 35},		  {"Eric", 49},		  {"Johnson", 59},		  };vector<personnel> all_employee(8);sort (first,first+5);sort (second,second+5);merge (first,first+5,second,second+5,v.begin());cout << "The resulting vector contains:";for_each(v.begin(), v.end(), [](int val)->void {cout << val << " ";}); cout << '\n';sort (it_depart.begin(), it_depart.end(), sort_object);cout << "After Sorted, IT depart:" << endl;for_each(it_depart.begin(), it_depart.end(), [](personnel emp)->void {cout << emp.name << " " << emp.age << endl;}); cout << '\n';sort (hr_depart.begin(), hr_depart.end(), sort_object);cout << "After Sorted, HR depart:" << endl;for_each(hr_depart.begin(), hr_depart.end(), [](personnel emp)->void {cout << emp.name << " " << emp.age << endl;}); cout << '\n';merge(it_depart.begin(), it_depart.end(), hr_depart.begin(), hr_depart.end(), all_employee.begin(), sort_object);cout << "After Merged, All employee:" << endl;cout << "All Employee:" << endl;for_each(all_employee.begin(), all_employee.end(), [](personnel emp)->void {cout << emp.name << " " << emp.age << endl;}); cout << '\n';return 0;
}

代码运行结果屏幕输出

The resulting vector contains:5 10 10 15 20 20 25 30 40 50
After Sorted, IT depart:
Allison 25
Sam 29
John 30
Alice 39After Sorted, HR depart:
Tommy 35
Michael 40
Eric 49
Johnson 59After Merged, All employee:
All Employee:
Allison 25
Sam 29
John 30
Tommy 35
Alice 39
Michael 40
Eric 49
Johnson 59

inplace_merge

合并两个连续的排序范围：[first,middle) 和 [middle,last)，将结果放入合并的排序范围 [first,last) 中。

第一个版本使用operator< 来比较元素，

template <class BidirectionalIterator>  
void inplace_merge (BidirectionalIterator first, BidirectionalIterator middle, BidirectionalIterator last);

第二个版本使用comp 来比较元素。两个范围中的元素应已根据相同的标准（operator< 或 comp）进行排序。结果范围也按此排序。

template <class BidirectionalIterator, class Compare>  
void inplace_merge (BidirectionalIterator first, BidirectionalIterator middle,         BidirectionalIterator last, Compare comp);

该函数保留具有等效值的元素的相对顺序，第一个范围中的元素位于第二个范围中的等效元素之前。

使用实列

#include <iostream>
#include <algorithm>
#include <vector>using namespace std;struct personnel {string  name;int     age;
};void print_personnel(personnel person) 
{ cout << person.name << " " << person.age << endl; }struct sort_class {bool operator() (personnel lf, personnel lr) { return (lf.age < lr.age);}
} sort_object;int main () {int first[] = {5,10,15,20,25};int second[] = {50,40,30,2,1};vector<personnel> it_depart = {{"John", 30},{"Allison", 25},		  {"Sam", 29},		  {"Alice", 39},		  };vector<personnel> hr_depart = {{"Michael", 40},{"Tommy", 18},		  {"Eric", 19},		  {"Johnson", 59},		  };vector<personnel> all_employee(8);vector<personnel>::iterator it_emp;vector<int> v(10);vector<int>::iterator it;sort (first,first+5);sort (second,second+5);it=copy (first, first+5, v.begin());copy (second,second+5,it);cout << "Before merge:";for_each(v.begin(), v.end(), [](int val)->void{cout << val << " ";});cout << endl;inplace_merge (v.begin(),v.begin()+5,v.end());cout << " After merge:";for_each(v.begin(), v.end(), [](int val)->void{cout << val << " ";});cout << endl;sort (it_depart.begin(), it_depart.end(), sort_object);sort (hr_depart.begin(), hr_depart.end(), sort_object);it_emp=copy (it_depart.begin(), it_depart.end(), all_employee.begin());copy (hr_depart.begin(), hr_depart.end(), it_emp);cout << "Employee before merge:" << endl;for_each(all_employee.begin(), all_employee.end(), [](personnel emp)->void {cout << emp.name << " " << emp.age << endl;});cout << endl;inplace_merge (all_employee.begin(), all_employee.begin()+4, all_employee.end(), sort_object);cout << "Employee after merge:" << endl;for_each(all_employee.begin(), all_employee.end(), [](personnel emp)->void {cout << emp.name << " " << emp.age << endl;});cout << endl;return 0;
}

代码运行结果屏幕输出

Before merge:5 10 15 20 25 1 2 30 40 50After merge:1 2 5 10 15 20 25 30 40 50
Employee before merge:
Allison 25
Sam 29
John 30
Alice 39
Tommy 18
Eric 19
Michael 40
Johnson 59Employee after merge:
Tommy 18
Eric 19
Allison 25
Sam 29
John 30
Alice 39
Michael 40
Johnson 59

set_difference

构造一个排序范围，其元素是，排序范围 [first1,last1)和排序范围 [first2,last2)之间的差。

两个集合的差是由第一个集合中存在，但第二个集合中不存在的元素形成的。函数复制的元素始终来自第一个范围，且顺序相同。

对于支持值多次出现的容器，差异包括给定值在第一个范围中出现的次数减去第二个范围中匹配元素的数量（保留顺序）。

第一个版本使用operator< 来比较元素
第二个版本使用comp 来比较元素。如果 (!(a<b) && !(b<a)) 或 if (!comp(a,b) && !comp(b,a))，则 a 和 b 两个元素被视为等效。

范围中的元素应已根据相同的标准（operator< 或 comp）进行排序。结果范围也按此排序。

使用实列

#include <iostream>
#include <algorithm>
#include <vector>using namespace std;struct personnel {string  name;int     age;
};void print_personnel(personnel person) { cout << person.name << " " << person.age << endl; }struct sort_class {bool operator() (personnel lf, personnel lr) { return (lf.age < lr.age);}
} sort_object;struct equal_class {bool operator() (personnel lf, personnel lr) { return ((lf.name != lr.name) || (lf.age != lr.age));}
} equal_object;int main () {vector<int> first = {15,10,50,20,25,2};vector<int> second = {50,40,30,20,10};vector<personnel> it_depart = {{"John", 30},{"Allison", 25},		  {"Sam", 29},		  {"Alice", 30},		  };vector<personnel> all_employee = {{"John", 30},{"Allison", 25},		  {"Sam", 29},		  {"Alice", 39},		  {"Tommy", 35},		  {"Eric", 49},		  {"Johnson", 59},		  };vector<personnel> other_employee(all_employee.size());vector<int> v(11); vector<int>::iterator it;vector<personnel>::iterator it_emp;sort (first.begin(), first.end()); sort (second.begin(), second.end());it=set_difference (first.begin(), first.end(),second.begin(), second.end(), v.begin());v.resize(it-v.begin());cout << "The difference has " << (v.size()) << " elements:\n";for_each(v.begin(), v.end(), [](int val)->void {cout << val << " ";});cout << endl;sort (it_depart.begin(), it_depart.end(), sort_object); sort (all_employee.begin(), all_employee.end(), sort_object);it_emp=set_difference (all_employee.begin(), all_employee.end(),it_depart.begin(), it_depart.end(), other_employee.begin(), equal_object);other_employee.resize(it_emp - other_employee.begin());cout << "Other employee:" << endl;for_each(other_employee.begin(), other_employee.end(), [](personnel emp)->void {cout << emp.name << " " << emp.age << endl;});cout << endl;return 0;
}

代码运行结果屏幕输出

The difference has 3 elements:
2 15 25
Other employee:
Tommy 35
Alice 39
Eric 49
Johnson 59

堆

make_heap

重新排列 [first,last) 范围内的元素，使它们形成堆。

堆是一种组织元素序列的方法，它允许在任何时刻，重复地快速检索具有最高值的元素（使用 pop_heap），同时允许快速插入新元素（使用 push_heap）。

具有最高值的元素始终是第一个元素。其他元素的顺序取决于特定的实现，但所有与堆相关的函数都是一致的。

使用operator<（对于第一个版本）或
comp（对于第二个版本）来比较元素：具有最高值的元素是与范围中的每个其他元素进行比较时将返回 false 的元素。

标准容器适配器priority_queue自动调用make_heap、push_heap和pop_heap来维护容器的堆属性。

使用实列

#include <iostream>
#include <algorithm>
#include <vector>using namespace std;int main () {vector<int> v = {10,20,30,5,15};make_heap (v.begin(),v.end());cout << "Initial heap: ";for_each(v.begin(),v.end(), [](int val)->void {cout << val << " ";});cout << endl;cout << "initial max heap   : " << v.front() << '\n';pop_heap(v.begin(),v.end()); cout << "after pop_head heap: ";for_each(v.begin(),v.end(), [](int val)->void {cout << val << " ";});cout << endl;v.pop_back();cout << "after pop_back vector: ";for_each(v.begin(),v.end(), [](int val)->void {cout << val << " ";});cout << endl;cout << "max heap after pop : " << v.front() << '\n';v.push_back(99); cout << "after push_back vector: ";for_each(v.begin(),v.end(), [](int val)->void {cout << val << " ";});cout << endl;push_heap (v.begin(),v.end());cout << "after push_head heap: ";for_each(v.begin(),v.end(), [](int val)->void {cout << val << " ";});cout << endl;cout << "max heap after push: " << v.front() << '\n';return 0;
}

代码运行结果屏幕输出:

Initial heap: 30 20 10 5 15
initial max heap   : 30
after pop_head heap: 20 15 10 5 30
after pop_back vector: 20 15 10 5
max heap after pop : 20
after push_back vector: 20 15 10 5 99
after push_head heap: 99 20 10 5 15
max heap after push: 99

sort_heap

将堆范围 [first,last) 中的元素按升序或降序排序。

第一个版本使用operator<来比较元素，
第二个版本使用comp来比较元素，这应该与构造堆时使用的相同。

该序列失去了其作为堆的属性。

使用实列

#include <iostream> 
#include <algorithm>
#include <vector>using namespace std;struct personnel {string  name;int     age;
};struct sort_class {bool operator() (personnel lf, personnel lr) {return ((lf.name < lr.name) || ((lf.name == lr.name) && (lf.age < lr.age)));}
} sort_object;int main () {vector<int> v = {10,20,30,5,15};vector<personnel> depart = {{"John", 30},{"Allison", 25},		  {"Sam", 29},		  {"Sam", 49},		  {"Alice", 39},		  };personnel new_incomer = {"Alice", 29};make_heap (v.begin(),v.end());cout << "initial max heap   : " << v.front() << '\n';pop_heap (v.begin(),v.end());v.pop_back();cout << "max heap after pop : " << v.front() << '\n';v.push_back(99);push_heap (v.begin(),v.end());cout << "max heap after push: " << v.front() << '\n';sort_heap (v.begin(),v.end());cout << "final sorted range :";for_each(v.begin(),v.end(), [](int val)->void {cout << val << " ";});;cout << endl;//make_heap (depart.begin(), depart.end(), sort_object);cout << "After make_heap:" << endl;cout << "initial max heap   : " << depart.front().name << " " << depart.front().age << '\n';for_each(depart.begin(), depart.end(), [](personnel emp)->void {cout << " [ " << emp.name << " " << emp.age << " ] ";}); cout << '\n';depart.push_back(new_incomer);cout << "After push_back:" << endl;for_each(depart.begin(), depart.end(), [](personnel emp)->void {cout << " [ " << emp.name << " " << emp.age << " ] ";}); cout << '\n';push_heap (depart.begin(), depart.end(), sort_object);cout << "After make_heap:" << endl;cout << "max heap after push: " << depart.front().name << " " << depart.front().age << '\n';for_each(depart.begin(), depart.end(), [](personnel emp)->void {cout << " [ " << emp.name << " " << emp.age << " ] ";}); cout << '\n';sort_heap (depart.begin(), depart.end(), sort_object);cout << "final sorted range :" << endl;for_each(depart.begin(), depart.end(), [](personnel emp)->void {cout << " [ " << emp.name << "," << emp.age << " ] ";});cout << endl;return 0;
}

代码运行结果屏幕输出:

initial max heap   : 30
max heap after pop : 20
max heap after push: 99
final sorted range :5 10 15 20 99
After make_heap:
initial max heap   : Sam 49[ Sam 49 ]  [ John 30 ]  [ Sam 29 ]  [ Allison 25 ]  [ Alice 39 ]
After push_back:[ Sam 49 ]  [ John 30 ]  [ Sam 29 ]  [ Allison 25 ]  [ Alice 39 ]  [ Alice 29 ]
After make_heap:
max heap after push: Sam 49[ Sam 49 ]  [ John 30 ]  [ Sam 29 ]  [ Allison 25 ]  [ Alice 39 ]  [ Alice 29 ]
final sorted range :[ Alice,29 ]  [ Alice,39 ]  [ Allison,25 ]  [ John,30 ]  [ Sam,29 ]  [ Sam,49 ]