stl的算法(一)：对序列进行只读操作(查找、搜索等)
Stl的算法的不更改序列操作主要有以下12项：
for_each、find、find_if、find_end、find_first_of、adjacent_find
count、count_if、mismatch、equal、search、search_n
1、 for_each:遍历某个区域内每个元素
原型：template <class InputIterator, class Function>
Function for_each (InputIterator first, InputIterator last, Function f);
形参：first、last确定那个一个区域；f是函数指针，必须重载()
例子：// for_each example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
void myfunction (int i) {
cout << " " << i;
}
struct myclass {
void operator() (int i) {cout << " " << i;}
} myobject;
int main () {
vector<int> myvector;
myvector.push_back(10);
myvector.push_back(20);
myvector.push_back(30);
cout << "myvector contains:";
for_each (myvector.begin(), myvector.end(), myfunction);
// or:
cout << "\nmyvector contains:";
for_each (myvector.begin(), myvector.end(), myobject);
cout << endl;
return 0;
}
2、 find:返回在迭代器指定的范围内第一个匹配的值，如果没有找到返回last
原型：template <class InputIterator, class T>
InputIterator find ( InputIterator first, InputIterator last, const T& value );
形参：见for_each
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;
}
3、 find_if
原型：template <class InputIterator, class Predicate>
InputIterator find_if ( InputIterator first, InputIterator last, Predicate pred );
形参：同上
功能：变量first和end间的区域，如果调用pred都返回false，则函数返回end；如果返回true，
则直接break，返回当前iterator。这里查找的是一个element
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;
}
4、 find_end:
原型：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 );
功能：搜索first2，last2在first1，last1中最后一次匹配的位置
形参: first1、end1和first2、end2确定一个序列，pred的含义和上面的函数雷同
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;
}
5、 find_first_of:
原型：template <class ForwardIterator1, class ForwardIterator2>
ForwardIterator1 find_first_of ( ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2 );
template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
ForwardIterator1 find_first_of ( ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred );
功能：搜索first2，last2在first1，last1中第一次匹配的位置
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;
}
6、 adjacent_find：
原型：template <class ForwardIterator>
ForwardIterator adjacent_find ( ForwardIterator first, ForwardIterator last );
template <class ForwardIterator, class BinaryPredicate>
ForwardIterator adjacent_find ( ForwardIterator first, ForwardIterator last,
BinaryPredicate pred );
功能：查找连续重复的元素
形参：见find
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
7、 count：
原型：template <class InputIterator, class T>
typename iterator_traits<InputIterator>::difference_type
count ( ForwardIterator first, ForwardIterator last, const T& value );
功能：统计value在first、end间出现的次数
例子：
// count algorithm example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main () {
int mycount;
// counting elements in array:
int myints[] = {10,20,30,30,20,10,10,20}; // 8 elements
mycount = (int) count (myints, myints+8, 10);
cout << "10 appears " << mycount << " times.\n";
// counting elements in container:
vector<int> myvector (myints, myints+8);
mycount = (int) count (myvector.begin(), myvector.end(), 20);
cout << "20 appears " << mycount << " times.\n";
return 0;
}
8、 count_if
原型：template <class InputIterator, class Predicate>
typename iterator_traits<InputIterator>::difference_type
count_if ( ForwardIterator first, ForwardIterator last, Predicate pred );
功能：返回满足pred条件的元素个数
例子：// count_if example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool IsOdd (int i) { return ((i%2)==1); }
int main () {
int mycount;
vector<int> myvector;
for (int i=1; i<10; i++) myvector.push_back(i); // myvector: 1 2 3 4 5 6 7 8 9
mycount = (int) count_if (myvector.begin(), myvector.end(), IsOdd);
cout << "myvector contains " << mycount << " odd values.\n";
return 0;
}
9、 mismatch
原型：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 );
功能：返回first2和end2在first1和end1内不匹配的位置
例子：// mismatch algorithm example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool mypredicate (int i, int j) {
return (i==j);
}
int main () {
vector<int> myvector;
for (int i=1; i<6; i++) myvector.push_back (i*10); // myvector: 10 20 30 40 50
int myints[] = {10,20,80,320,1024}; // myints: 10 20 80 320 1024
pair<vector<int>::iterator,int*> mypair;
// using default comparison:
mypair = mismatch (myvector.begin(), myvector.end(), myints);
cout << "First mismatching elements: " << *mypair.first;
cout << " and " << *mypair.second << endl;;
mypair.first++; mypair.second++;
// using predicate comparison:
mypair = mismatch (mypair.first, myvector.end(), mypair.second, mypredicate);
cout << "Second mismatching elements: " << *mypair.first;
cout << " and " << *mypair.second << endl;;
return 0;
}
Output：First mismatching elements: 30 and 80
Second mismatching elements: 40 and 320
10、equal
原型：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 );
功能：比较从first2开始的一个序列是否和first1、end1的序列相等
例子：
// equal algorithm example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool mypredicate (int i, int j) {
return (i==j);
}
int main () {
int myints[] = {20,40,60,80,100}; // myints: 20 40 60 80 100
vector<int>myvector (myints,myints+5); // myvector: 20 40 60 80 100
// using default comparison:
if (equal (myvector.begin(), myvector.end(), myints))
cout << "The contents of both sequences are equal." << endl;
else
cout << "The contents of both sequences differ." << endl;
myvector[3]=81; // myvector: 20 40 60 81 100
// using predicate comparison:
if (equal (myvector.begin(), myvector.end(), myints, mypredicate))
cout << "The contents of both sequences are equal." << endl;
else
cout << "The contents of both sequences differ." << endl;
return 0;
}
11、search
原型：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 );
功能：和find_end类似，但不是end，而是first
例子：#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool mypredicate (int i, int j) {
return (i==j);
}
int main () {
vector<int> myvector;
vector<int>::iterator it;
// set some values: myvector: 10 20 30 40 50 60 70 80 90
for (int i=1; i<10; i++) myvector.push_back(i*10);
// using default comparison:
int match1[] = {40,50,60,70};
it = search (myvector.begin(), myvector.end(), match1, match1+4);
if (it!=myvector.end())
cout << "match1 found at position " << int(it-myvector.begin()) << endl;
else
cout << "match1 not found" << endl;
// using predicate comparison:
int match2[] = {20,30,50};
it = search (myvector.begin(), myvector.end(), match2, match2+3, mypredicate);
if (it!=myvector.end())
cout << "match2 found at position " << int(it-myvector.begin()) << endl;
else
cout << "match2 not found" << endl;
return 0;
}
12、search_n
原型：template <class ForwardIterator, class Size, class T>
ForwardIterator search_n ( ForwardIterator first, ForwardIterator last,
Size count, const T& value );
template <class ForwardIterator, class Size, class T, class BinaryPredicate>
ForwardIterator search_n ( ForwardIterator first, ForwardIterator last,
Size count, const T& value, BinaryPredicate pred );
功能：在某个范围内搜索值；如果没找到返回end
例子：
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool mypredicate (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 = search_n (myvector.begin(), myvector.end(), 2, 30);
if (it!=myvector.end())
cout << "two 30s found at position " << int(it-myvector.begin()) << endl;
else
cout << "match not found" << endl;
// using predicate comparison:
it = search_n (myvector.begin(), myvector.end(), 2, 10, mypredicate);
if (it!=myvector.end())
cout << "two 10s found at position " << int(it-myvector.begin()) << endl;
else
cout << "match not found" << endl;
return 0;
}