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 keyint *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 keyiter = lower_bound(a, a + 12, 19);assert( *iter == 19 );//in this case the answer is the sameint* 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 keyiter_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 keyiter_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> inlinevoid __CLRCALL_OR_CDECL _Distance2(_InIt _First, _InIt _Last, _Diff& _Off,input_iterator_tag){// add to _Off distance between input iteratorsfor (; _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.