STL算法 ------ 根据第n个元素排序

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1. nth_element( b, n, e ) 对n位置的元素进行比较，大的放后面，小的放前面，n必须是迭代器指向输入的元素；

2. nth_element(b, n, e, p )

3.对比：partition() 算法

#include <iostream>#include <algorithm>#include <iterator>#include <vector>#include <list>#include <deque>#include <functional>using namespace std;template<typename T>void Print(const T& t){for(typename T::const_iterator itr=t.begin(); itr!=t.end(); ++itr){cout<<*itr<<' ';}cout<<endl;}int main( int argc, char** argv ){deque<int> deq;for(int i=3; i<=7; ++i){deq.push_back(i);}for(int i=2; i<=6; ++i){deq.push_back(i);}for(int i=1; i<=5; ++i){deq.push_back(i);}Print(deq);nth_element(deq.begin(), deq.begin()+3, deq.end());Print(deq);copy(deq.begin(), deq.begin()+4, ostream_iterator<int>(cout, " "));cout<<endl;nth_element(deq.begin(), deq.end()-4, deq.end());copy(deq.end()-4, deq.end(), ostream_iterator<int>(cout, " "));cout<<endl;nth_element(deq.begin(), deq.begin()+3, deq.end(), greater<int>());copy(deq.begin(), deq.begin()+4, ostream_iterator<int>(cout, " "));cout<<endl;deque<int>::iterator pos;pos = partition(deq.begin(), deq.end(), bind2nd(less_equal<int>(), 3));copy(deq.begin(), pos, ostream_iterator<int>(cout, " "));return 0;}

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