泛型算法系列5:lower_bound()&&upper_bound()

#include <algorithm> #include <vector> #include <iostream> #include <functional> #include <assert.h> using namespace std; template <class Type> void print_elements(Type elem) { cout << elem << ","; } void (*pfi)(int) = print_elements; int main() { int a[] = {29,23,20,22,17,15,26,51,19,12,35,40}; vector<int> vec(a, a + 12); sort(a, a + 12); cout << "after sort." << endl; for_each(a, a + 12, pfi); //when use upper, we got iter which point to the data after key int *iter = upper_bound(a, a + 12, 19); assert( *iter == 20 ); //when use lower, when we find the same value,we got iter which the data equal to key iter = lower_bound(a, a + 12, 19); assert( *iter == 19 ); //in this case the answer is the same int* iter_new = upper_bound(a, a + 12, 18); //int* iter_new = lower_bound(a, a + 12, 18); assert( *iter_new == 19 ); cout << "/n#####################################/n" << endl; sort(vec.begin(), vec.end(), greater<int>()); for_each(vec.begin(), vec.end(), pfi); vector<int>::iterator iter_vec; //when use upper, we got iter which point to the data after key iter_vec = upper_bound(vec.begin(), vec.end(), 27, greater<int>()); assert( *iter_vec == 26 ); //when use lower, we got iter which point to the data before key iter_vec = lower_bound(vec.begin(), vec.end(), 27, greater<int>()); assert( *iter_vec == 26 ); cout << "/n#####################################/n" << endl; vec.insert(iter_vec, 27); for_each(vec.begin(), vec.end(), pfi); return 0; } /************************************************************************/ /**/ template<class _FwdIt, class _Ty, class _Diff> inline _FwdIt _Upper_bound(_FwdIt _First, _FwdIt _Last, const _Ty& _Val, _Diff *) { // find first element that _Val is before, using operator< _Distance(_First, _Last, _Count); for (; 0 < _Count; ) { // divide and conquer, find half that contains answer _Diff _Count2 = _Count / 2; _FwdIt _Mid = _First; std::advance(_Mid, _Count2); _DEBUG_ORDER_SINGLE(_Mid, _Last, false); if (!_DEBUG_LT(_Val, *_Mid)) _First = ++_Mid, _Count -= _Count2 + 1; else _Count = _Count2; } return (_First); } /************************************************************************/ /************************************************************************/ /**/ template<class _FwdIt, class _Ty, class _Diff> inline _FwdIt _Lower_bound(_FwdIt _First, _FwdIt _Last, const _Ty& _Val, _Diff *) { // find first element not before _Val, using operator< _DEBUG_ORDER_SINGLE(_First, _Last, true); _Diff _Count = 0; _Distance(_First, _Last, _Count); for (; 0 < _Count; ) { // divide and conquer, find half that contains answer _Diff _Count2 = _Count / 2; _FwdIt _Mid = _First; std::advance(_Mid, _Count2); _DEBUG_ORDER_SINGLE(_Mid, _Last, false); if (_DEBUG_LT(*_Mid, _Val)) _First = ++_Mid, _Count -= _Count2 + 1; else _Count = _Count2; } return (_First); } /************************************************************************/ /************************************************************************/ /* */ template<class _InIt, class _Diff> inline void __CLRCALL_OR_CDECL _Distance2(_InIt _First, _InIt _Last, _Diff& _Off, input_iterator_tag) { // add to _Off distance between input iterators for (; _First != _Last; ++_First) ++_Off; } /************************************************************************/

注释：

binary_search：判断是否存在某个对象
lower_bound: 返回>=对象的第一个位置，lower_bound(2)=3, lower_bound(3)=3
目标对象存在即为目标对象的位置,不存在则为后一个位置.
upper_bound: 返回>对象的第一个位置, upper_bound(2)=3,upper_bound(3)=4
无论是否存在都为后一个位置.