C++ STL源码学习之算法篇(四)
++__first; __len = __len - __half - 1; } } return __first; } template
pair<_ForwardIter, _ForwardIter> __equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Distance*) { _Distance __len = 0; distance(__first, __last, __len); _Distance __half; _ForwardIter __middle, __left, __right; while (__len > 0) { __half = __len >> 1; __middle = __first; advance(__middle, __half); ///先采用类似lower_bound的方法找到一个等于val的值 if (*__middle < __val) { __first = __middle; ++__first; __len = __len - __half - 1; } else if (__val < *__middle) __len = __half; else { ///找到后分区间调用lower和upper_bound找到__left和__right的位置 ///这样做要比一开始就调用lower_bound和upper_bound高效一些 __left = lower_bound(__first, __middle, __val); advance(__first, __len); __right = upper_bound(++__middle, __first, __val); return pair<_ForwardIter, _ForwardIter>(__left, __right); } } ///说明未找到 return pair<_ForwardIter, _ForwardIter>(__first, __first); } ///二分查找，依赖lower_bound实现 template
bool binary_search(_ForwardIter __first, _ForwardIter __last, const _Tp& __val) { _ForwardIter __i = lower_bound(__first, __last, __val); return __i != __last && !(__val < *__i); } /// merge, with and without an explicitly supplied comparison function. template
_OutputIter merge(_InputIter1 __first1, _InputIter1 __last1, _InputIter2 __first2, _InputIter2 __last2, _OutputIter __result) { while (__first1 != __last1 && __first2 != __last2) { if (*__first2 < *__first1) { *__result = *__first2; ++__first2; } else { *__result = *__first1; ++__first1; } ++__result; } return copy(__first2, __last2, copy(__first1, __last1, __result)); } /// Set algorithms: includes, set_union, set_intersection, set_difference, /// set_symmetric_difference. All of these algorithms have the precondition /// that their input ranges are sorted and the postcondition that their output /// ranges are sorted. ///集合类操作需要保证集合元素是已排序的，算是根据已排序 ///序列的特性实现的 template
bool includes(_InputIter1 __first1, _InputIter1 __last1, _InputIter2 __first2, _InputIter2 __last2) { while (__first1 != __last1 && __first2 != __last2) if (*__first2 < *__first1) return false; else if(*__first1 < *__first2) ++__first1; else ++__first1, ++__first2; return __first2 == __last2; } ///和merge很相似，但不会重复包含两个区间的公共元素 template
_OutputIter set_union(_InputIter1 __first1, _InputIter1 __last1, _InputIter2 __first2, _InputIter2 __last2, _OutputIter __result) { while (__first1 != __last1 && __first2 != __last2) { if (*__first1 < *__first2) { *__result = *__first1; ++__first1; } else if (*__first2 < *__first1) { *__result = *__first2; ++__first2; } else { *__result = *__first1; ++__first1; ++__first2; } ++__result; } return copy(__first2, __last2, copy(__first1, __last1, __result)); } ///得到两个序列的交集 template
_OutputIter set_intersection(_InputIter1 __first1, _InputIter1 __last1, _InputIter2 __first2, _InputIter2 __last2, _OutputIter __result) { while (__first1 != __last1 && __first2 != __last2) if (*__first1 < *__first2) ++__first1; else if (*__first2 < *__first1) ++__first2; else { *__result = *__first1; ++__first1; ++__first2; ++__result; } return __result; } ///得到两个序列的差集 template
_OutputIter set_difference(_InputIter1 __first1, _InputIter1 __last1, _InputIter2 __first2, _InputIter2 __last2, _OutputIter __result) { while (__first1 != __last1 && __first2 != __last2) if (*__first1 < *__first2) { *__result = *__first1; ++__first1; ++__result; } else if (*__first2 < *__first1) ++__first2; else { ++__first1; ++__first2; } return copy(__first1, __last1, __result); } ///两个集合的对称差集 template
_OutputIter set_symmetric_difference(_InputIter1 __first1, _InputIter1 __last1, _InputIter2 __first2, _InputIter2 __last2, _OutputIter __result) { while (__first1 != __last1 && __first2 != __last2) if (*__first1 < *__first2) { *__result = *__first1; ++__first1; ++__result; } else if (*__first2 < *__first1) { *__result = *__first2; ++__first2; ++__result; } else { ++__first1; ++__first2; } return copy(__first2, __last2, copy(__first1, __last1, __result)); } /// next_permutation and prev_permutation ///在当前序列中，从尾端往前寻找两个相邻元素，前一个记为*__i，后一个记为*__ii， ///并且满足*__i < *__ii。然后再从尾端寻找另一个元素*__j，如果满足*__j，即将 ///第__i个元素与第__j个元素对调，并将第__ii个元素之后（包括__ii）的所有元素颠倒排序， ///即求出下一个序列了。 template
bool next_permutation(_BidirectionalIter __first, _BidirectionalIter __last) { if (__first == __last) return false; _BidirectionalIter __i = __first; ++__i; if (__i == __last) return false; __i = __last; --__i; for(;;) { _BidirectionalIter __ii = __i; --__i; if (*__i < *__ii) { _BidirectionalIter __j = __last; while (!(*__i < *--__j)) {} iter_swap(__i, __j); reverse(__ii, __last); return true; } if (__i == __first) { reverse(__first, __last); return false; } } } template
bool prev_permutation(_BidirectionalIter __first, _BidirectionalIter __last) { if (__first == __last) return false; _BidirectionalIter __i = __first; ++__i; if (__i == __last) return false; __i = __last; --__i; for(;;) { _BidirectionalIter __ii = __i; --__i; if (*__ii < *__i) { _BidirectionalIter __j = __last; while (!(*--__j < *__i)) {} iter_swap(__i, __j); reverse(__ii, __last); return true; } if (__i == __first) { reverse(__first, __last); return false; } } } template
_InputIter find_first_of(_InputIter __first1, _InputIter __last1, _ForwardIter __first2, _ForwardIter __last2) { for ( ; __first1 != __last1; ++__first1) for (_ForwardIter __iter = __first2; __iter != __last2; ++__iter) if (*__first1 == *__iter) return __first1; return __last1; } /// find_end, Search [first2, last2) as a subsequence in [first1, last1), and return /// the *last* possible match. Note that find_end for bidirectional iterators /// is much faster than for forward iterators. /// find_end for forward iterators. template
_ForwardIter1 __find_end(_ForwardIter1 __first1, _ForwardIter1 __last1, _ForwardIter2 __first2, _ForwardIter2 __last2, forward_iterator_tag, forward_iterator_tag) { if (__first2 == __last2) return __last1; else { _ForwardIter1 __result = __last1; while (1) { _ForwardIter1 __new_result = search(__first1, __last1, __first2, __last2); if (__new_result == __last1) return __result; else { __result = __new_result; __first1 = __new_result; ++__first1; } } } } /// find_end f