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C++ 算法 中的 partial_sort函数
C++算法 partial_sort()函数用于重新排列range [first，last)中的元素，以这样的方式对第一个和中间的元素进行排序，而在中间和中间的元素进行排序最后将以不确定的顺序。
partial_sort - 语法
default (1) template <class RandomAccessIterator> void partial_sort (RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last); custom (2) template <class RandomAccessIterator, class Compare> void partial_sort (RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last, Compare comp);
partial_sort - 参数
first:一个随机访问迭代器，指向要部分排序的参数中的第一个元素。
last:一个随机访问迭代器，指向要部分排序的参数中的最后一个元素。
middle:一个随机访问迭代器，指向要排序的子参数中最后一个元素之后的那个。
comp :用户定义的二进制谓词函数，该函数接受两个参数，如果两个参数顺序正确，则返回true，否则返回false。它遵循严格的弱排序来对元素进行排序。
partial_sort - 返回值
没有
partial_sort - 例子1
让我们看一个简单的示例来演示partial_sort()的用法:
#include <iostream> #include <vector> #include <algorithm> using namespace std; int main() { vector<int> v = {3, 1, 4, 2, 5}; cout<<"Before sorting: "; for_each(v.begin(), v.end(), [](int x) { cout << x << " "; }); partial_sort(v.begin(), v.begin() + 2, v.end()); cout<<"\nAfter sorting: "; for_each(v.begin(), v.end(), [](int x) { cout << x << " "; }); return 0; }
输出:
Before sorting: 3 1 4 2 5 After sorting: 1 2 4 3 5
partial_sort - 例子2
让我们看另一个简单的例子:
#include <iostream> //std::cout #include <algorithm> //std::partial_sort #include <vector> //std::vector using namespace std; bool myfunction (int i,int j) { return (i<j); } int main () { int myints[] = {9,8,7,6,5,4,3,2,1}; vector<int> myvector (myints, myints+9); //using default comparison (operator <): partial_sort (myvector.begin(), myvector.begin()+5, myvector.end()); //using function as comp partial_sort (myvector.begin(), myvector.begin()+5, myvector.end(),myfunction); //print out content: cout << "myvector contains:"; for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it) cout << ' ' << *it; cout << '\n'; return 0; }
输出:
myvector contains: 1 2 3 4 5 9 8 7 6
partial_sort - 例子3
让我们来看一个默认版本的简单示例:
#include <iostream> #include <algorithm> #include <functional> #include <vector> using namespace std ; int main() { const int VECTOR_SIZE = 8 ; //Define a template class vector of int typedef vector<int> IntVector ; //Define an iterator for template class vector of strings typedef IntVector::iterator IntVectorIt ; IntVector Numbers(VECTOR_SIZE) ; IntVectorIt start, end, it ; //Initialize vector Numbers Numbers[0] = 4 ; Numbers[1] = 10; Numbers[2] = 70 ; Numbers[3] = 30 ; Numbers[4] = 10; Numbers[5] = 69 ; Numbers[6] = 96 ; Numbers[7] = 7; start = Numbers.begin() ; //location of first //element of Numbers end = Numbers.end() ; //one past the location //last element of Numbers cout << "Before calling partial_sort\n" << endl ; //print content of Numbers cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ; //sort the smallest 4 elements in the sequence partial_sort(start, start+4, end) ; cout << "After calling partial_sort\n" << endl ; cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ; return 0; }
输出:
Before calling partial_sort
Numbers { 4 10 70 30 10 69 96 7 }
After calling partial_sort
Numbers { 4 7 10 10 70 69 96 30 }
partial_sort - 例子4
让我们看一个自定义(谓词)版本的简单示例:
#include <iostream> #include <algorithm> #include <functional> #include <vector> using namespace std ; int main() { const int VECTOR_SIZE = 8 ; //Define a template class vector of int typedef vector<int> IntVector ; //Define an iterator for template class vector of strings typedef IntVector::iterator IntVectorIt ; IntVector Numbers(VECTOR_SIZE) ; IntVectorIt start, end, it ; //Initialize vector Numbers Numbers[0] = 4 ; Numbers[1] = 10; Numbers[2] = 70 ; Numbers[3] = 30 ; Numbers[4] = 10; Numbers[5] = 69 ; Numbers[6] = 96 ; Numbers[7] = 7; start = Numbers.begin() ; //location of first //element of Numbers end = Numbers.end() ; //one past the location //last element of Numbers cout << "Before calling partial_sort\n" << endl ; //print content of Numbers cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ; //sort the smallest 4 elements in the sequence partial_sort(start, start+4, end, less<int>()) ; cout << "After calling partial_sort\n" << endl ; cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ; return 0; }
输出:
Before calling partial_sort
Numbers { 4 10 70 30 10 69 96 7 }
After calling partial_sort
Numbers { 4 7 10 10 70 69 96 30 }
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