泛型算法系列13:equal_range()

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#算法 #iterator #search #vector #output #stream

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本文展示了一个使用C++标准库函数equal_range的示例，该函数用于查找已排序序列中等于给定值的所有元素范围。示例包括了对数组和vector的操作，并展示了如何处理存在及不存在于序列中的搜索值。

#include <algorithm> #include <vector> #include <utility> #include <iostream> #include<functional> using namespace std; /* generates: array element sequence after sort: 12 15 17 19 20 22 23 26 29 35 40 51 equal_range result of search for value 23: *ia_iter.first: 23 *ia_iter.second: 26 equal_range result of search for absent value 21: *ia_iter.first: 22 *ia_iter.second: 22 vector element sequence after sort: 51 40 35 29 26 23 22 20 19 17 15 12 equal_range result of search for value 26: *ivec_iter.first: 26 *ivec_iter.second: 23 equal_range result of search for absent value 21: *ivec_iter.first: 20 *ivec_iter.second: 20 */ /************************************************************************/ /* */ template<class _InIt, class _Diff> inline void __CLRCALL_OR_CDECL my_Advance(_InIt& _Where, _Diff _Off) { // increment iterator by offset, input iterators for (; 0 < _Off; --_Off) ++_Where; } /************************************************************************/ template<class _FwdIt, class _Ty> inline pair<_FwdIt, _FwdIt> my_equal_range(_FwdIt _First, _FwdIt _Last, const _Ty& _Val) { // find range equivalent to _Val, using operator< return (my_Equal_range(_First, _Last, _Val, _Dist_type(_First))); } template<class _FwdIt, class _Ty, class _Diff> inline pair<_FwdIt, _FwdIt> my_Equal_range(_FwdIt _First, _FwdIt _Last, const _Ty& _Val, _Diff *) { // find range equivalent to _Val, using operator< _DEBUG_ORDER_SINGLE(_First, _Last, true); _Diff _Count = 0; _Distance(_First, _Last, _Count); for (; 0 < _Count; ) { // divide and conquer, check midpoint _Diff _Count2 = _Count / 2; _FwdIt _Mid = _First; std::advance(_Mid, _Count2); _DEBUG_ORDER_SINGLE(_Mid, _Last, false); if (_DEBUG_LT(*_Mid, _Val)) { // range begins above _Mid, loop _First = ++_Mid; _Count -= _Count2 + 1; } else if (_Val < *_Mid) _Count = _Count2; // range in first half, loop else { // range straddles mid, find each end and return _FwdIt _First2 = lower_bound(_First, _Mid, _Val); std::advance(_First, _Count); _FwdIt _Last2 = upper_bound(++_Mid, _First, _Val); return (pair<_FwdIt, _FwdIt>(_First2, _Last2)); } } return (pair<_FwdIt, _FwdIt>(_First, _First)); // empty range } int main() { int ia[] = { 29,23,20,22,17,15,26,51,19,12,35,40 }; vector< int > ivec( ia, ia+12 ); ostream_iterator< int > ofile( cout, " " ); sort( &ia[0], &ia[12] ); cout << "array element sequence after sort:/n"; copy( ia, ia+12, ofile ); cout << "/n/n"; pair< int*,int* > ia_iter; ia_iter = my_equal_range( &ia[0], &ia[12], 23 ); cout << "equal_range result of search for value 23:/n/t" << "*ia_iter.first: " << *ia_iter.first << "/t" << "*ia_iter.second: " << *ia_iter.second << "/n/n"; ia_iter = equal_range( &ia[0], &ia[12], 21 ); cout << "equal_range result of search for " << "absent value 21:/n/t" << "*ia_iter.first: " << *ia_iter.first << "/t" << "*ia_iter.second: " << *ia_iter.second << "/n/n"; sort( ivec.begin(), ivec.end(), greater<int>() ); cout << "vector element sequence after sort:/n"; copy( ivec.begin(), ivec.end(), ofile ); cout << "/n/n"; typedef vector< int>::iterator iter_ivec; pair< iter_ivec, iter_ivec > ivec_iter; ivec_iter = equal_range( ivec.begin(), ivec.end(), 26, greater<int>() ); cout << "equal_range result of search for value 26:/n/t" << "*ivec_iter.first: " << *ivec_iter.first << "/t" << "*ivec_iter.second: " << *ivec_iter.second ; ivec_iter = equal_range( ivec.begin(), ivec.end(), 21, greater<int>() ); cout << "equal_range result of search for " << "absent value 21:/n/t" << "*ivec_iter.first: " << *ivec_iter.first << "/t" << "*ivec_iter.second: " << *ivec_iter.second ; return 0; } /************************************************************************/ /* */ template<class _Ty, class _Elem = char, class _Traits = char_traits<_Elem> > class ostream_iterator : public _Outit { // wrap _Ty inserts to output stream as output iterator public: typedef _Elem char_type; typedef _Traits traits_type; typedef basic_ostream<_Elem, _Traits> ostream_type; #if _SECURE_SCL typedef _Range_checked_iterator_tag _Checked_iterator_category; #endif ostream_iterator(ostream_type& _Ostr, const _Elem *_Delim = 0) : _Myostr(&_Ostr), _Mydelim(_Delim) { // construct from output stream and delimiter } ostream_iterator<_Ty, _Elem, _Traits>& operator=(const _Ty& _Val) { // insert value into output stream, followed by delimiter *_Myostr << _Val; if (_Mydelim != 0) *_Myostr << _Mydelim; return (*this); } ostream_iterator<_Ty, _Elem, _Traits>& operator*() { // pretend to return designated value return (*this); } ostream_iterator<_Ty, _Elem, _Traits>& operator++() { // pretend to preincrement return (*this); } ostream_iterator<_Ty, _Elem, _Traits> operator++(int) { // pretend to postincrement return (*this); } protected: static void _Xran() { // report an out_of_range error _THROW(out_of_range, "invalid ostream_iterator"); } const _Elem *_Mydelim; // pointer to delimiter string (NB: not freed) ostream_type *_Myostr; // pointer to output stream }; /************************************************************************/