stl的算法(一)：对序列进行只读操作(查找、搜索等)

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;

}