nth_element

template <class RandomAccessIterator>
  void nth_element ( RandomAccessIterator first, RandomAccessIterator nth,
                     RandomAccessIterator last );

template <class RandomAccessIterator, class Compare>
  void nth_element ( RandomAccessIterator first, RandomAccessIterator nth,
                     RandomAccessIterator last, Compare comp );

Sort element in range

Parameters

first, last

Random-Access iterators to the initial and final positions of the sequence to be used. The range used is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
Notice that in this function, these are not consecutive parameters, but the first and third ones.

nth

Random-Access iterator pointing to the location within the range [first,last) that will have the sorted element.

comp

Comparison function object that, taking two values of the same type than those contained in the range, returns true if the first argument goes before the second argument in the specific strict weak ordering it defines, and false otherwise.

Return value

Example

// nth_element example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool myfunction (int i,int j) { return (i<j); }
int main () {
  vector<int> myvector;
  vector<int>::iterator it;
  // set some values:
  for (int i=1; i<10; i++) myvector.push_back(i);   // 1 2 3 4 5 6 7 8 9
  random_shuffle (myvector.begin(), myvector.end());
  // using default comparison (operator <):
  nth_element (myvector.begin(), myvector.begin()+5, myvector.end());
  // using function as comp
  nth_element (myvector.begin(), myvector.begin()+5, myvector.end(),myfunction);
  // print out content:
  cout << "myvector contains:";
  for (it=myvector.begin(); it!=myvector.end(); ++it)
    cout << " " << *it;
  cout << endl;
  return 0;
}

myvector contains: 3 1 4 2 5 6 9 7 8

Complexity

See also