STL学习笔记（变序性算法）

变序性算法改变元素的次序，但不改变元素值。

这些算法不能用于关联式容器，因为在关联式容器中，元素有一定的次序，不能随意变动。

逆转元素次序

void

reverse(BidirectionalIterator beg,BidirectionalIterator end)

OutputIterator

reverse_copy(BidirectionalIterator sourceBeg,BidirectionalIterator sourceEnd,

OutputIterator destBeg)

1.reverce()会将区间[beg,end)内的元素全部逆序

2.reverse_copy()是reverse()跟copy()的组合

下面这个程序展示reverse()和reverse_copy()的用法

 #include <iterator>
 #include "algostuff.hpp"
 using namespace std;
 
 int main()
 {
     vector<int> coll;
     INSERT_ELEMENTS(coll,,);
     PRINT_ELEMENTS(coll,"coll: ");
     reverse(coll.begin(),coll.end());
     PRINT_ELEMENTS(coll,"coll: ");
     reverse(coll.begin()+,coll.end()-);
     PRINT_ELEMENTS(coll,"coll: ");
     reverse_copy(coll.begin(),coll.end(),ostream_iterator<int>(cout," "));
     cout<<endl;
 }

旋转(Rotating)元素次序

1.旋转序列内的元素

void

rotate(ForwardIterator beg,ForwardIterator newBeg,

ForwardIterator end)

1.将区间[beg,end)内的元素进行旋转，执行后*newBeg成为新的第一元素

2.调用者必须确保newBeg是[beg,end)内的一个有效位置，否则会引发未定义的行为

以下程序示范如何使用rotate()

 #include "algostuff.hpp"
 using namespace std;
 
 int main()
 {
     vector<int> coll;
     INSERT_ELEMENTS(coll,,);
     PRINT_ELEMENTS(coll,"coll: ");
     rotate(coll.begin(),coll.begin()+,coll.end());
     PRINT_ELEMENTS(coll,"one left: ");
     rotate(coll.begin(),coll.end()-,coll.end());
     PRINT_ELEMENTS(coll,"two right: ");
     rotate(coll.begin(),find(coll.begin(),coll.end(),),coll.end());
     PRINT_ELEMENTS(coll,"4 first: ");
 }

2.复制并同时旋转元素

OutputIterator

rotate_copy(ForwardIterator sourceBeg,ForwardIterator newBeg,

ForwardIterator sourceEnd,

OutputIterator destBeg)

这是copy()和rotate()的组合

以下程序示范rotate_copy()的用法

 #include <iterator>
 #include "algostuff.hpp"
 using namespace std;
 
 int main()
 {
     set<int> coll;
     INSERT_ELEMENTS(coll,,);
     PRINT_ELEMENTS(coll);
     set<int>::iterator pos=coll.begin();
     advance(pos,);
     rotate_copy(coll.begin(),pos,coll.end(),ostream_iterator<int>(cout," "));
     cout<<endl;
     pos=coll.end();
     advance(pos,-);
     rotate_copy(coll.begin(),pos,coll.end(),ostream_iterator<int>(cout," "));
     cout<<endl;
     rotate_copy(coll.begin(),coll.find(),coll.end(),ostream_iterator<int>(cout," "));
     cout<<endl;
 }

排列元素(Permuting)元素

bool

next_permutation(BidirectionalIterator beg,

BidirectionalIterator end)

bool

prev_permutation(BidirectionalIterator beg,

BidirectionalIterator end)

1.next_permutation()会改变区间[beg,end)内的元素次序，使他们符合“下一个排列次序”

2.prev_permutation()会改变区间[beg,end)内的元素次序，是他们符合“上一个排列次序”

下面这个例子展示利用next_permutation()和prev_permutation()将所有元素的所有可能排列的过程

 #include "algostuff.hpp"
 using namespace std;
 
 int main()
 {
     vector<int> coll;
     INSERT_ELEMENTS(coll,,);
     PRINT_ELEMENTS(coll,"on entry: ");
     while(next_permutation(coll.begin(),coll.end()))
         PRINT_ELEMENTS(coll," ");
     PRINT_ELEMENTS(coll,"afterward: ");
     while(prev_permutation(coll.begin(),coll.end()))
         PRINT_ELEMENTS(coll," ");
     PRINT_ELEMENTS(coll,"now: ");
     while(prev_permutation(coll.begin(),coll.end()))
         PRINT_ELEMENTS(coll," ");
     PRINT_ELEMENTS(coll,"afterward: ");
 }

重排元素(Shuffling,搅乱次序)

void

random_shuffle(RandomAccessIterator beg,RandomAccessIterator end)

void

random_shuffle(RandomAccessIterator beg,RandomAccessIterator end,

RandomFunc& op)

1.第一形式使用一个均匀分布随机数产生器来打乱区间[beg,end)内的元素次序

2.第二形式使用op打乱区间[beg,end)内的元素次序。

以下程序示范如何调用random_shuffle()来打乱元素次序

 #include <cstdlib>
 #include "algostuff.hpp"
 using namespace std;
 
 class MyRandom
 {
 public:
     ptrdiff_t operator()(ptrdiff_t max)
     {
         double tmp;
         tmp=static_cast<double>(rand())/static_cast<double>(RAND_MAX);
         return static_cast<ptrdiff_t>(tmp * max);
     }
 };
 
 int main()
 {
     vector<int> coll;
     INSERT_ELEMENTS(coll,,);
     PRINT_ELEMENTS(coll,"coll: ");
     random_shuffle(coll.begin(),coll.end());
     PRINT_ELEMENTS(coll,"shuffled: ");
     sort(coll.begin(),coll.end());
     PRINT_ELEMENTS(coll,"sorted: ");
     MyRandom rd;
     random_shuffle(coll.begin(),coll.end(),rd);
     PRINT_ELEMENTS(coll,"shuffled: ");
 }

将元素向前搬移

BidirectionalIterator

partition(BidirectionalIterator beg,

BidirectionalIterator end,

UnaryPredicate op)

BidirectionalIterator

stable_partition(BidirectionalIterator beg,

BidirectionalIterator end,

UnaryPredicate op)

1.这两种算法将区间[beg,end)中造成以下一元判断式：op(elem)结果为true的元素向前端移动

2.stable_partition()会保持元素之间的相对次序。

以下程序示范partition()和stable_partition()的用法以及两者的区别

 #include "algostuff.hpp"
 using namespace std;
 
 int main()
 {
     vector<int> coll1;
     vector<int> coll2;
     INSERT_ELEMENTS(coll1,,);
     INSERT_ELEMENTS(coll2,,);
     PRINT_ELEMENTS(coll1,"coll1: ");
     PRINT_ELEMENTS(coll2,"coll2: ");
     cout<<endl;
     vector<int>::iterator pos1,pos2;
     pos1=partition(coll1.begin(),coll1.end(),not1(bind2nd(modulus<int>(),)));
     pos2=stable_partition(coll2.begin(),coll2.end(),not1(bind2nd(modulus<int>(),)));
     PRINT_ELEMENTS(coll1,"coll1: ");
     cout<<"first odd element: "<<*pos1<<endl;
     PRINT_ELEMENTS(coll2,"coll1: ");
     cout<<"first odd elements: "<<*pos2<<endl;
     PRINT_ELEMENTS(coll2,"coll2: ");
 }