STLalgorithm算法partition_point,stable_partition(44)
partition_point原型:
std::partition_point
template <class ForwardIterator, class UnaryPredicate>
ForwardIterator partition_point (ForwardIterator first, ForwardIterator last,
UnaryPredicate pred);
该函数返回范围内第一个不符合pred(即返回值为false)的元素的迭代器.
范围内的元素应该已经进行过划分,即使用partition进行划分。否则可能会出错!
该函数优化了查找的次数。
其行为类似如下(类似于二分查找):
template <class ForwardIterator, class UnaryPredicate> ForwardIterator partition_point (ForwardIterator first, ForwardIterator last, UnaryPredicate pred) { auto n = distance(first,last); while (n>0) { ForwardIterator it = first; auto step = n/2; std::advance (it,step); if (pred(*it)) { first=++it; n-=step+1; } else n=step; } return first; }
一个简单的例子:
#include <iostream> #include <vector> #include <array> #include <algorithm> using namespace std; int main(){ vector<int> vi{8,5,10,7,1,3,5,8,9,13}; cout<<"vi="; for_each(vi.begin(),vi.end(),[](int i){cout<<i<<" ";}); cout<<endl; if(is_partitioned(vi.begin(),vi.end(),[](int n){return n%2==0;})) cout<<"v1 is a partitioned!"<<endl; else cout<<"v1 not a partitioned!"<<endl; auto it=partition(vi.begin(),vi.end(),[](int n){return n%2==0;}); cout<<"after auto it=partition(vi.begin(),vi.end(),[](int n){return n%2==0;}); "<<endl; cout<<"vi="; for_each(vi.begin(),vi.end(),[](int i){cout<<i<<" ";}); cout<<endl; if(is_partitioned(vi.begin(),vi.end(),[](int n){return n%2==0;})) cout<<"v1 is a partitioned!"<<endl; else cout<<"v1 not a partitioned!"<<endl; cout<<"*it="<<*it<<endl; auto it2=partition_point(vi.begin(),vi.end(),[](int n){return n%2==0;}); cout<<"auto it2=partition_point(vi.begin(),vi.end(),[](int n){return n%2==0;});"<<endl; cout<<"it2="<<*it2<<endl; }
运行结果:
返回值和partition是一样的。
stable_partition原型:
std::stable_partition
template <class BidirectionalIterator, class UnaryPredicate> BidirectionalIterator stable_partition (BidirectionalIterator first, BidirectionalIterator last, UnaryPredicate pred);
该函数对范围内的元素进行稳定划分。
返回值为第一个返回false的元素的迭代器,如果没有,则返回last.
和partition是有区别的,当然在数值上是看不出来的。区别为:
稳定和不稳定,这对数值没有什么用,但对于多属性的对象就有用了。 如以下组合序列,按括号外的数排序,括号内是另一个属性, 1(1), 3(2), 5(3), 5(4), 7(5), 9(6) , 7(7) 稳定排序后 1(1), 3(2), 5(3), 5(4), 7(5), 7(7) , 9(6) 两个5和两个7的相对位置不变, 不稳定排序后,可以是5(4), 5(3)或7(7), 7(5)
感谢:http://zhidao.baidu.com/link?url=wpPsrq1rg5IQioAZ_afz4Qd5drgWSUfiw-GU1GcK_ur3cwNlLCgzwVIR5q0sEdsmS_H0ajKWM97wVsJcgK6uUuH-cl9_ZZzE4wRdTMi1M7e
一个简单的例子:
#include <iostream> #include <vector> #include <array> #include <algorithm> using namespace std; int main(){ vector<int> vi{8,5,10,7,1,3,5,8,9,13}; cout<<"vi="; for_each(vi.begin(),vi.end(),[](int i){cout<<i<<" ";}); cout<<endl; if(is_partitioned(vi.begin(),vi.end(),[](int n){return n%2==0;})) cout<<"v1 is a partitioned!"<<endl; else cout<<"v1 not a partitioned!"<<endl; auto it=stable_partition(vi.begin(),vi.end(),[](int n){return n%2==0;}); cout<<"after auto it=stable_partition(vi.begin(),vi.end(),[](int n){return n%2==0;}); "<<endl; cout<<"vi="; for_each(vi.begin(),vi.end(),[](int i){cout<<i<<" ";}); cout<<endl; if(is_partitioned(vi.begin(),vi.end(),[](int n){return n%2==0;})) cout<<"v1 is a partitioned!"<<endl; else cout<<"v1 not a partitioned!"<<endl; cout<<"*it="<<*it<<endl; }
运行截图:
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//写的错误或者不好的地方请多多指导,可以在下面留言或者点击左上方邮件地址给我发邮件,指出我的错误以及不足,以便我修改,更好的分享给大家,谢谢。
转载请注明出处:http://blog.csdn.net/qq844352155
author:天下无双
Email:coderguang@gmail.com
2014-9-22
于GDUT
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