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C++ 算法 中的 partial_sort_copy函数
C++算法 partial_sort_copy()函数类似于partial_sort()函数，该函数用于重新排列range [first，last)中的元素，这样第一和中间之间的元素将是排序后，中间和最后一个元素之间的顺序将不确定。但是partial_sort_copy()函数将结果放入新的参数[result_first，result_last)。
partial_sort_copy - 语法
default (1) template <class InputIterator, class RandomAccessIterator> RandomAccessIterator partial_sort_copy (InputIterator first,InputIterator last, RandomAccessIterator result_first, RandomAccessIterator result_last); custom (2) template <class InputIterator, class RandomAccessIterator, class Compare> RandomAccessIterator partial_sort_copy (InputIterator first,InputIterator last, RandomAccessIterator result_first, RandomAccessIterator result_last, Compare comp);
partial_sort_copy - 参数
first:一个输入迭代器，它指向源参数中要部分排序的第一个元素。
last:一个随机访问迭代器，它指向要部分排序的源参数中的最后一个元素。
result_first :指向已排序目标参数中第一个元素的随机访问迭代器。
result_last :指向已排序目标参数中过去的最后一个元素的随机访问迭代器。
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。
partial_sort_copy - 返回值
它返回一个迭代器寻址，该迭代器寻址结果序列中最后写入的元素之后的元素。
partial_sort_copy - 例子1
让我们看一个简单的示例，以演示partial_sort_copy()的用法:
#include <iostream> //std::cout #include <algorithm> //std::partial_sort_copy #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 (5); //using default comparison (operator <): partial_sort_copy (myints, myints+9, myvector.begin(), myvector.end()); //using function as comp partial_sort_copy (myints, myints+9, myvector.begin(), 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
partial_sort_copy - 例子2
让我们看一下默认版本的另一个简单示例:
#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) ; IntVector Result(4) ; 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_copy\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 Numbers //and copy the results in Result partial_sort_copy(start, end, Result.begin(), Result.end()) ; cout << "After calling partial_sort_copy\n" << endl ; cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ; cout << "Result { " ; for(it = Result.begin(); it != Result.end(); it++) cout << *it << " " ; cout << " }\n" << endl ; return 0; }
输出:
Before calling partial_sort_copy
Numbers { 4 10 70 30 10 69 96 7 }
After calling partial_sort_copy
Numbers { 4 10 70 30 10 69 96 7 }
Result { 4 7 10 10 }
partial_sort_copy - 例子3
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) ; IntVector Result(4) ; 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_copy\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 Numbers //and copy the results in Result partial_sort_copy(start, end, Result.begin(),Result.end(),less<int>()); cout << "After calling partial_sort_copy\n" << endl ; cout << "Numbers { " ; for(it = start; it != end; it++) cout << *it << " " ; cout << " }\n" << endl ; cout << "Result { " ; for(it = Result.begin(); it != Result.end(); it++) cout << *it << " " ; cout << " }\n" << endl ; return 0; }
输出:
Before calling partial_sort_copy
Numbers { 4 10 70 30 10 69 96 7 }
After calling partial_sort_copy
Numbers { 4 10 70 30 10 69 96 7 }
Result { 4 7 10 10 }
partial_sort_copy - 例子4
让我们看另一个例子:
#include <algorithm> #include <vector> #include <functional> #include <iostream> using namespace std; vector<int>::iterator it; void print(vector<int> & v) { for (it = v.begin(); it != v.end(); it++) { cout << *it << ' '; } cout << '\n'; } int main() { vector<int> v0{4, 2, 5, 1, 3}; vector<int> v1{10, 11, 12}; vector<int> v2{10, 11, 12, 13, 14, 15, 16}; cout << "v0 : "; print(v0); cout << "v1 : "; print(v1); cout << "v2 : "; print(v2); it = partial_sort_copy(v0.begin(), v0.end(), v1.begin(), v1.end()); cout << "Writing v0 to v1 in ascending order gives: "; print(v1); it = partial_sort_copy(v0.begin(), v0.end(), v2.begin(), v2.end(), std::greater<int>()); cout << "Writing v0 to v2 in descending order gives: "; print(v2); return 0; }
输出:
v0 : 4 2 5 1 3 v1 : 10 11 12 v2 : 10 11 12 13 14 15 16 Writing v0 to v1 in ascending order gives: 1 2 3 Writing v0 to v2 in descending order gives: 5 4 3 2 1 15 16
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