C++ STL 算法精选之查找篇
1.查找类算法
adjacent_find(first,last);
查找区间[first,last)内第一次出现连续的两个相等的元素，并返回指向第一个元素的迭代器，连续元素之间的比较，默认是==
adjacent_find(first,last,pred);
用途如上，但是元素之间的比较是通过函数pred来完成，pred接受两个容器内元素类型的元素，返回bool值
函数原型：
template <class ForwardIterator>
ForwardIterator adjacent_find ( ForwardIterator first, ForwardIterator last )
{
ForwardIterator next=first; ++next;
if (first != last)
while (next != last)
if (*first++ == *next++) // or: if (pred(*first++,*next++)), for the pred version
return first;
return last;
}
例子：
// adjacent_find example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool myfunction (int i, int j) {
return (i==j);
}
int main () {
int myints[] = {10,20,30,30,20,10,10,20};
vector<int> myvector (myints,myints+8);
vector<int>::iterator it;
// using default comparison:
it = adjacent_find (myvector.begin(), myvector.end());
if (it!=myvector.end())
cout << "the first consecutive repeated elements are: " << *it << endl;
//using predicate comparison:
it = adjacent_find (++it, myvector.end(), myfunction);
if (it!=myvector.end())
cout << "the second consecutive repeated elements are: " << *it << endl;
return 0;
}
Output:
the first consecutive repeated elements are: 30
the second consecutive repeated elements are: 10
find(first,last,value);
查找区间[first,last)之间内值为value的元素，返回迭代器类型，若没找到，则返回迭代器末尾end 函数原型：
template<class InputIterator, class T>
InputIterator find ( InputIterator first, InputIterator last, const T& value )
{
for ( ;first!=last; first++) if ( *first==value ) break;
return first;
}
例子：// find example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main () {
int myints[] = { 10, 20, 30 ,40 };
int * p;
// pointer to array element:
p = find(myints,myints+4,30);
++p;
cout << "The element following 30 is " << *p << endl;
vector<int> myvector (myints,myints+4);
vector<int>::iterator it;
// iterator to vector element:
it = find (myvector.begin(), myvector.end(), 30);
++it;
cout << "The element following 30 is " << *it << endl;
return 0;
}
Output:
The element following 30 is 40
The element following 30 is 40
find_if(first,last,pred);
返回区间[first,last)内第一个使pred函数返回为真的元素的迭代器，否则返回last注意：pred接受一个参数函数原型：
template<class InputIterator, class Predicate>
InputIterator find_if ( InputIterator first, InputIterator last, Predicate pred )
{
for ( ; first!=last ; first++ ) if ( pred(*first) ) break;
return first;
}
例子：// find_if example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool IsOdd (int i) {
return ((i%2)==1);
}
int main () {
vector<int> myvector;
vector<int>::iterator it;
myvector.push_back(10);
myvector.push_back(25);
myvector.push_back(40);
myvector.push_back(55);
it = find_if (myvector.begin(), myvector.end(), IsOdd);
cout << "The first odd value is " << *it << endl;
return 0;
}
Output:
The first odd value is 25
find_first_of(first1,last1,first2,last2);
find_first_of(first1,last1,first2,last2,pred);
返回一个迭代器，使得[first2,last2)之中任意一个元素第一次出现在区间[first1,last1)中。
默认比较为==,当然也可以自己定义pred函数(接受2个参数)，返回bool型 函数原型：
template<class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 find_first_of ( ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2)
{
for ( ; first1 != last1; ++first1 )
for (ForwardIterator2 it=first2; it!=last2; ++it)
if (*it==*first1) // or: if (comp(*it,*first)) for the pred version
return first1;
return last1;
}
例子：// find_first_of example
#include <iostream>
#include <algorithm>
#include <cctype>
#include <vector>
using namespace std;
bool comp_case_insensitive (char c1, char c2) {
return (tolower(c1)==tolower(c2));
}
int main () {
int mychars[] = {'a','b','c','A','B','C'};
vector<char> myvector (mychars,mychars+6);
vector<char>::iterator it;
int match[] = {'A','B','C'};
// using default comparison:
it = find_first_of (myvector.begin(), myvector.end(), match, match+3);
if (it!=myvector.end())
cout << "first match is: " << *it << endl;
// using predicate comparison:
it = find_first_of (myvector.begin(), myvector.end(),
match, match+3, comp_case_insensitive);
if (it!=myvector.end())
cout << "first match is: " << *it << endl;
return 0;
}
Output:
First match is: A
First match is: a
find_end(first1,last1,first2,last2);
find_end(first1,last1,first2,last2,pred);
返回一个元素迭代器，使得在区间[first1,last1)中最后一次出现[fiest2,last2),
默认比较为==，当然也可以写自己的比较函数pred,接受两个参数，返回bool值函数原型：
template<class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 find_end ( ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2)
{
ForwardIterator1 it1, limit, ret;
ForwardIterator2 it2;
limit=first1; advance(limit,1+distance(first1,last1)-distance(first2,last2));
ret=last1;
while (first1!=limit)
{
it1 = first1; it2 = first2;
while (*it1==*it2) // or: while (pred(*it1,*it2)) for the pred version
{ ++it1; ++it2; if (it2==last2) {ret=first1;break;} }
++first1;
}
return ret;
}
例子：// find_end example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool myfunction (int i, int j) {
return (i==j);
}
int main () {
int myints[] = {1,2,3,4,5,1,2,3,4,5};
vector<int> myvector (myints,myints+10);
vector<int>::iterator it;
int match1[] = {1,2,3};
// using default comparison:
it = find_end (myvector.begin(), myvector.end(), match1, match1+3);
if (it!=myvector.end())
cout << "match1 last found at position " << int(it-myvector.begin()) << endl;
int match2[] = {4,5,1};
// using predicate comparison:
it = find_end (myvector.begin(), myvector.end(), match2, match2+3, myfunction);
if (it!=myvector.end())
cout << "match2 last found at position " << int(it-myvector.begin()) << endl;
return 0;
}
Output:
Match found at position 5
Match found at position 3
