Rotate () function analysis of STL source code analysis

Rotate () function analysis of STL source code analysis

What is the rotate () function capable of?

Http://www.cplusplus.com/reference/algorithm/rotate/?kw=rotate

The above is only approximate, the source code is given below:

Rotate and rotate_copy, and their auxiliary functionstemplate <class _euclideanringelement>_ Euclideanringelement __GCD (_euclideanringelement __m, _euclideanringelement __n) {while (__n!)    = 0) {_euclideanringelement __t = __m% __n;    __m = __n;  __n = __t; } return __m;} Template <class _forwarditer, class _distance>_forwarditer __rotate (_forwarditer __first, _FORW Arditer __middle, _forwarditer __last, _distance*, Forward_  Iterator_tag) {if (__first = = __middle) return __last;  if (__last = = __middle) return __first;  _forwarditer __first2 = __middle;    Do {swap (*__first++, *__first2++);  if (__first = = __middle) __middle = __first2;  } while (__first2! = __last);  _forwarditer __new_middle = __first;  __first2 = __middle;    while (__first2! = __last) {swap (*__first++, *__first2++); if (__first = = __middle) __middle = __firsT2;  else if (__first2 = = __last) __first2 = __middle; } return __new_middle;}                            Template <class _bidirectionaliter, class _distance>_bidirectionaliter __rotate (_bidirectionaliter __first,                            _bidirectionaliter __middle, _bidirectionaliter __last, _distance*, Bidirectional_iterator_tag) {__stl_requires (_bidirectionaliter, _mutable_b  Idirectionaliterator);  if (__first = = __middle) return __last;  if (__last = = __middle) return __first;  __reverse (__first, __middle, Bidirectional_iterator_tag ());  __reverse (__middle, __last, Bidirectional_iterator_tag ());  while (__first! = __middle && __middle! = __last) Swap (*__first++, *--__last);    if (__first = = __middle) {__reverse (__middle, __last, Bidirectional_iterator_tag ());  return __last;    } else {__reverse (__first, __middle, Bidirectional_iterator_tag ());  return __first; }}/* all ElemEnts. |...front. |  ... | ^ 0 Offset ^ Middle ^ last*/template <class _randomaccessiter, Class _distance, class _tp>_randomaccessiter _ _rotate (_randomaccessiter __first, _randomaccessiter __middle, _random Accessiter __last, _distance *, _TP *) {__stl_requires (_randomaccessiter, _mutable_randomacces  Siterator); _distance __n = __last-__first; The number of all elements _distance __k = __middle-__first;          The front elements _distance __l = __n-__k;  The back elements _randomaccessiter __result = __first + (__last-__middle);  if (__k = = 0) return __last;    else if (__k = = __l) {swap_ranges (__first, __middle, __middle);  return __result;  } _distance __d = __GCD (__n, __k);    for (_distance __i = 0; __i < __d; __i++) {_tp __tmp = *__first;    _randomaccessiter __p = __first; if (__k < __l) {/* In this case, elements of the BAck part was more than the front ' s. */for (_distance __j = 0; __j < __l/__d; __j++) {if (__p > __first + __l) {*__p = * (__p-__)          L);        __p-= __l;        } *__p = * (__p + __k);      __p + = __k;          }} else {for (_distance __j = 0; __j < __k/__d-1; __j + +) {if (__p < __last-__k) {          *__p = * (__p + __k);        __p + = __k;        } *__p = * (__p-__l);      __p-= __l;    }} *__p = __tmp;  ++__first; } return __result;}

Want to debug themselves, anyway the code is not long, copy a little modification can be used.

Seriously read the above source code, I will find that the changes I made very very small.

I added a macro definition switch, DEBUG, wrote a show_data function, easy to see the changes in the data

/************************************************programmer:eofe-mail:[email protected]date : 2015.04.02file:rotate.cpp*************************************************/#include <iostream> #include <vector> #include <algorithm> #define debugusing namespace Std;int __gcd (int __m, int __n) {int __t = 0;while (__ n! = 0) {__t = __m% __n;__m = __n;__n = __t;} return __m;} void Show_data (Vector<int>::iterator first, Vector<int>::iterator last) {for (; first! = Last; first++) {cout << *first << "";} cout << Endl << Endl;}  /* all elements. |...front. |  ... | ^ 0 Offset ^ Middle ^ last*/void My_rotate (Vector<int>::iterator __first, Vector<int>::it Erator __middle, Vector<int>::iterator __last) {int __n = __last-__first;//The number of all Elem Entsint __k = __middle-__first;          The front elementsint __l = __n-__k; The back elementsif (__k = = 0) return; int __d = __GCD (__n, __k); #ifdef debugvector<int>::iterator start = __first;cout << "The original data:" << endl;s How_data (Start, __last), #endifvector <int>::iterator __p;for (int __i = 0; __i < __d; __i++) {int __tmp = *__first ; __p = __first;if (__k < __l) {/* In this case, elements of the "back" is more than the front ' s.*/for (int __j = 0; __j < __l/__d; __j++) {/***it ' s so fantastic!! */if (__p > __first + __l) {*__p = * (__p-__l); __p-= __l;} *__p = * (__p + __k) __p + = __k; #ifdef debugcout << "I:" << __i << "J:" << __j << Endl;sho W_data (Start, __last), #endif}}else {for (int __j = 0; __j < __k/__d-1; __j++) {if (__p < __last-__k) {*__p = * (__p + __k); __p + = __k;} *__p = * (__p-__l); __p-= __l; #ifdef debugcout << "I:" << __i << "J:" << __j << endl;sh Ow_data (start, __last); #endif}}*__p = __tmp;++__first;} return;} int main () {vector<int> Myvector;//set some values;for (int i = 0; I < 9; i++) {myvector.push_back (i);} My_rotate (Myvector.begin (), Myvector.begin () + 3, Myvector.end ()), cout << "myvector contains:"; for (Vect        Or<int>::iterator it = Myvector.begin ();        It! = Myvector.end (); it++) {cout << "" << *it;} cout << Endl;return 0;}

Add the Show_data () it is very easy to perceptual first of all how the algorithm operation has a preliminary understanding.

The program author is very ingenious and does not use the extra memory, the rotate operation of the data in situ. STL authors, they're all Daniel.

Qaq I really feel I understand, but this place I do not know how to express the concise.

Why do you use GCD in that place? What is the specific meaning.

Pending Update ~

Rotate () function analysis of STL source code analysis