这里接着上篇stl非变易算法（一）进行总结。主要解析算法函数count、count_if、mismatch、equal、search、search_n以及find_end。给出算法函数的实现及測试用例。以下直接进入正题。
统计等于某值的容器元素个数count
count函数用于计算容器中某个给定值的出现次数。计算迭代区间[first,last)上等于val值的元素个数ret。返回计数。
//count算法函数的实现代码
template <class InputIterator, class T>
typename iterator_traits<InputIterator>::difference_type
count (InputIterator first, InputIterator last, const T& val)
{
typename iterator_traits<InputIterator>::difference_type ret = 0;
while (first!=last)
{
if (*first == val)
++ret;
++first;
}
return ret;
}//測试用例
#include <algorithm>
#include <list>
#include <iostream>
using namespace std;
int main(void)
{
list<int> l;
for(int i=0; i<100; i++)
l.push_back(i%20);
int num=0;
int value=9;
num=count(l.begin(), l.end(), value);
cout << "链表中元素等于value的元素个数为: "
<< num << endl;
return 0;
}
条件统计容器元素个数count_if
与count算法函数相似，count_if算法函数仅仅是使用谓词推断pred，统计迭代器区间[first,last)上满足条件的元素个数n，返回计数。
//count_if算法函数代码
template <class InputIterator, class UnaryPredicate>
typename iterator_traits<InputIterator>::difference_type
count_if (InputIterator first, InputIterator last, UnaryPredicate pred)
{
typename iterator_traits<InputIterator>::difference_type n = 0;
while (first!=last) {
if (pred(*first)) ++n;
++first;
}
return n;
}//測试用例
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
//是否为奇数
bool IsOdd (int i)
{
return ((i%2)==1);
}
int main ()
{
vector<int> v;
for (int i=1; i<10; i++)
v.push_back(i);
int mycount = count_if (v.begin(), v.end(), IsOdd);
cout << "v容器包括 " << mycount << " 奇数值。
"
;
return 0;
}
元素不匹配查找mismatch
mismatch算法函数比較两个序列，找出首个不匹配元素的位置。
找出迭代区间[first1,last1)上第一个元素i，他与迭代区间[first2,first2+(last1-first1))上的元素（first2+(i-first1))不相等（或不满足二元谓词pred条件）。通过pair返回这两个元素的迭代器。指示不匹配元素 的位置。
)
template <class InputIterator1, class InputIterator2>
pair<InputIterator1, InputIterator2>
mismatch (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2);
template <class InputIterator1, class InputIterator2, class BinaryPredicate>
pair<InputIterator1, InputIterator2>
mismatch (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, BinaryPredicate pred);- mismatch函数的模板类型选择了不同的符号InputIterator1和InputIterator2，表示可取不同的容器迭代器。
//mismatch算法函数的代码
template <class InputIterator1, class InputIterator2>
pair<InputIterator1, InputIterator2>
mismatch (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2 )
{
while ( (first1!=last1) && (*first1==*first2) ) // or: pred(*first1,*first2), for version 2
{ ++first1; ++first2; }
return std::make_pair(first1,first2);
} //測试用例
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
bool strEqual(const char* s1, const char* s2){
return strcmp(s1, s2) == 0 ? 1 : 0;
}
int main(void)
{
//初始化向量v1、v2
vector<int> v1, v2;
v1.push_back(2);
v1.push_back(0);
v1.push_back(0);
v1.push_back(6);
v2.push_back(2);
v2.push_back(0);
v2.push_back(0);
v2.push_back(7);
//v1和v2不匹配检查
pair<vector<int>::iterator, vector<int>::iterator> result1=
mismatch(v1.begin(), v1.end(), v2.begin());
if(result1.first == v1.end() && result1.second == v1.end())
cout << "v1和v2全然同样" << endl;
else
cout << "v1和v2不同样,不匹配的数是:
"
<< *result1.first << endl
<< *result1.second << endl << endl;
//初始化字符串s1、s2
char* s1[] = {"apple", "pear", "watermelon", "banana", "grape"};
char* s2[] = {"apple", "pears", "watermelons", "banana", "grape"};
//s1和s2不匹配检查
pair<char**, char**> result2=mismatch(s1, s1+5, s2, strEqual);
if(result2.first == s1+5 && result2.second ==s2+5)
cout << "s1和s2全然同样" << endl;
else
cout << "s1与s2不同样,不匹配的字符串为:
"
<< s1[result2.first -s1] << endl
<< s2[result2.second -s2] << endl << endl;
return 0;
}
元素相等推断equal
相似mismatch、equal算法函数也是逐一比較两个序列的元素是否相等，仅仅是equal函数返回true/false，不返回迭代器值。也是有例如以下两种使用原型。假设迭代区间[first1,last1)和迭代器区间[first2,first2+(last1-first1))上的元素相等（或满足二元谓词推断条件pred),返回true，否则返回false。
template <class InputIterator1, class InputIterator2>
bool equal (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2);
template <class InputIterator1, class InputIterator2, class BinaryPredicate>
bool equal (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, BinaryPredicate pred);//equal算法函数的代码
template <class InputIterator1, class InputIterator2>
bool equal ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2 )
{
while (first1!=last1) {
if (!(*first1 == *first2)) // or: if (!pred(*first1,*first2)), for version 2
return false;
++first1; ++first2;
}
return true;
}//測试用例
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
bool absEqual(int a, int b){
return (a== abs(b) || abs(a) == b) ? 1:0;
}
int main(void)
{
//初始化向量v1、v2
vector <int> v1(5);
vector <int> v2(5);
for(unsigned int i = 0; i < v1.size(); i++) {
v1[i] = i;
v2[i] = -1 * i;
}
//v1、v2相等检查
if(equal(v1.begin(), v1.end(), v2.begin(), absEqual))
cout << "v1和v2元素的绝对值全然相等" << endl;
else
cout << "v1和v2元素的绝对值不全然相等" << endl;
return 0;
}
子序列搜索search
search算法函数在一个序列中搜索与还有一个序列匹配的子序列。有例如以下两个原型。在迭代器区间[first1,last1)上找出与迭代器区间[first2,last2)全然匹配（或满足二元谓词推断pred）的子序列，返回子序列首个元素的迭代器值，或返回last1表示没有匹配的子序列。
template <class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);//search算法函数的代码
template<class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 search ( ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2)
{
if (first2==last2) return first1;
while (first1!=last1)
{
ForwardIterator1 it1 = first1;
ForwardIterator2 it2 = first2;
// or: while (pred(*it1,*it2)) for version 2
while (*it1==*it2) {
++it1; ++it2;
if (it2==last2) return first1;
if (it1==last1) return last1;
}
++first1;
}
return last1;
} //測试用例
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main(void)
{
//初始化向量v1={5, 6, 7, 8, 9 }
vector<int> v1;
v1.push_back(5);
v1.push_back(6);
v1.push_back(7);
v1.push_back(8);
v1.push_back(9);
//初始化向量v2={7, 8}
vector<int> v2;
v2.push_back(7);
v2.push_back(8);
//检查v2是否构成v1的子序列
vector<int>::iterator iterLocation;
iterLocation=search(v1.begin(), v1.end(), v2.begin(), v2.end());
//打印从v1[2]開始匹配
if(iterLocation != v1.end())
cout << "v2的元素包括在v1中,起始元素为"
<< "v1[" << iterLocation - v1.begin() << "]
";
else
cout << "v2的元素不包括在v1中" << endl;
return 0;
}
反复元素子序列搜索search_n
search_n算法函数搜索序列中是否有一系列元素值均为某个给定值的子序列。
有例如以下两个原型。分别在迭代器区间[first,last)上搜索是否有count个连续元素，其值均等于value（或满足谓词推断pred的条件）。返回子序列首元素的迭代器，或返回last表示没有反复元素的子序列。
template <class ForwardIterator, class Size, class T>
ForwardIterator search_n (ForwardIterator first, ForwardIterator last,
Size count, const T& val);
template <class ForwardIterator, class Size, class T, class BinaryPredicate>
ForwardIterator search_n ( ForwardIterator first, ForwardIterator last,
Size count, const T& val, BinaryPredicate pred ); //search_n算法函数的代码
template<class ForwardIterator, class Size, class T>
ForwardIterator search_n (ForwardIterator first, ForwardIterator last,
Size count, const T& val)
{
ForwardIterator it, limit;
Size i;
limit=first; std::advance(limit,std::distance(first,last)-count);
while (first!=limit)
{
it = first; i=0;
while (*it==val) // or: while (pred(*it,val)) for the pred version
{ ++it; if (++i==count) return first; }
++first;
}
return last;
} //測试用例
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main(void)
{
vector<int> v;
v.push_back(1);
v.push_back(8);
v.push_back(6);
v.push_back(6);
v.push_back(9);
vector<int>::iterator iLocation;
iLocation=search_n(v.begin(), v.end(), 2, 6);
if(iLocation != v.end())
cout << "在v中找到2个连续的元素6" << endl;
else
cout << "v中没有2个连续的元素6" << endl;
return 0;
} 
最后一个子序列搜索find_end
find_end算法函数在一个序列中搜索出最后一个与还有一序列匹配的子序列。有例如以下两个使用原型。
在迭代器区间[first1,last1)中搜索出与迭代器区间[first2,last2)元素匹配的子序列。返回首元素的迭代器或返回last1，表示没有子序列匹配。
template <class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred); //find_end函数实现
template<class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2)
{
if (first2==last2) return last1; // specified in C++11
ForwardIterator1 ret = last1;
while (first1!=last1)
{
ForwardIterator1 it1 = first1;
ForwardIterator2 it2 = first2;
while (*it1==*it2) { // or: while (pred(*it1,*it2)) for version (2)
++it1; ++it2;
if (it2==last2) { ret=first1; break; }
if (it1==last1) return ret;
}
++first1;
}
return ret;
}//測试用例
#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main(void)
{
//初始化向量v1={-5, 1, 2, -6, -8, 1, 2, -11}
vector<int> v1;
v1.push_back(-5);
v1.push_back(1);
v1.push_back(2);
v1.push_back(-6);
v1.push_back(-8);
v1.push_back(1);
v1.push_back(2);
v1.push_back(-11);
//初始化向量v2={1, 2}
vector<int> v2;
v2.push_back(1);
v2.push_back(2);
//v1中查找最后一个子序列v2
vector<int>::iterator iLocation;
iLocation=find_end(v1.begin(), v1.end(), v2.begin(), v2.end());
//打印子序列在v1的起始位置v[5]
if(iLocation != v1.end())
cout << "v1中找到最后一个匹配v2的子序列,位置在"
<< "v1[" << iLocation - v1.begin() << "]" << endl;
return 0;
} 
完结。
转载请注明出处：http://blog.csdn.net/lsh_2013/article/details/46849279