stl nth_element使用...

#include <algorithm>
#include <vector>
#include <ctime>
#include <iostream>
using namespace std;
const int MAX = 50;
int main(int argc, char *argv[])
{
vector<int> vec;
int each;
int count = 10;

srand((unsigned)time(NULL));

for(int i=0; i<count; i++)
{
each = rand() % MAX;
vec.push_back(each);
}

cout << "before nth_element: " << endl;
for(int i=0; i<count; i++)
cout << vec.at(i) << " ";
cout << endl;

nth_element(vec.begin(), vec.begin() + 5, vec.end());

cout << "after nth_element: " << endl;
for(int i=0; i<count; i++)
cout << vec.at(i) << " ";
cout << endl;
system("PAUSE");
return EXIT_SUCCESS;
}