STL 查找算法
要给出所有我们在本条款中所考虑到的，我们的从哪儿着手？下面的表格道出了一切。
| 你想知道的 | 使用的算法 | 使用的成员函数 | ||
|---|---|---|---|---|
| 在无序区间 | 在已序区间 | 在set或map上 | 在multiset或multimap上 | |
| 期望值是否存在？ | find | binary_search | count | find |
| 期望值是否存在？如果有，第一个等于这个值的对象在哪里？ | find | equal_range | find | find or lower_bound(see article) |
| 第一个不等于期望值的对象在哪里？ | find_if | lower_bound | lower_bound | lower_bound |
| 第一个等于期望值的对象在哪里？ | find_if | upper_bound | upper_bound | upper_bound |
| 有多少对象等于期望值？ | count | equal_range | count | count |
| 等于期望值的所有对象在哪里？ | find（迭代） | equal_range | equal_range | equal_range |
===============================================================================
Example
// equal_range example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
bool mygreater (int i,int j) { return (i>j); }
int main () {
int myints[] = {10,20,30,30,20,10,10,20};
vector<int> v(myints,myints+8); // 10 20 30 30 20 10 10 20
pair<vector<int>::iterator,vector<int>::iterator> bounds;
// using default comparison:
sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30
bounds=equal_range (v.begin(), v.end(), 20); // ^ ^
// using "mygreater" as comp:
sort (v.begin(), v.end(), mygreater); // 30 30 20 20 20 10 10 10
bounds=equal_range (v.begin(), v.end(), 20, mygreater); // ^ ^
cout << "bounds at positions " << int(bounds.first - v.begin());
cout << " and " << int(bounds.second - v.begin()) << endl;
return 0;
}
Output:
bounds ar positions 2 and 5
=================================================================
equal_range()
template< class ForwardIterator, class Type > pair< ForwardIterator, ForwardIterator > equal_range( ForwardIterator first, ForwardIterator last, const Type &value );
//返回pair ，若容器中存在搜索值，第一个返回by lower_bound(); 第二个 by upper_bound();
若容器中不存在搜索值，两个都返回by upper_bound(); template< class ForwardIterator, class Type, class Compare > pair< ForwardIterator, ForwardIterator > equal_range( ForwardIterator first, ForwardIterator last, const Type &value, Compare comp );
#include <algorithm>
#include <vector>
#include <utility>
#include <iostream>
#include<functional>
using namespace std;
/* generates:
array element sequence after sort:
12 15 17 19 20 22 23 26 29 35 40 51
equal_range result of search for value 23:
*ia_iter.first: 23 *ia_iter.second: 26
equal_range result of search for absent value 21:
*ia_iter.first: 22 *ia_iter.second: 22
vector element sequence after sort:
51 40 35 29 26 23 22 20 19 17 15 12
equal_range result of search for value 26:
*ivec_iter.first: 26 *ivec_iter.second: 23
equal_range result of search for absent value 21:
*ivec_iter.first: 20 *ivec_iter.second: 20
*/
int main()
{
int ia[] = { 29,23,20,22,17,15,26,51,19,12,35,40 };
vector< int > ivec( ia, ia+12 );
ostream_iterator< int > ofile( cout, " " );
sort( &ia[0], &ia[12] );
cout << "array element sequence after sort:\n";
copy( ia, ia+12, ofile ); cout << "\n\n";
pair< int*,int* > ia_iter;
ia_iter = equal_range( &ia[0], &ia[12], 23 );
cout << "equal_range result of search for value 23:\n\t"
<< "*ia_iter.first: " << *ia_iter.first << "\t"
<< "*ia_iter.second: " << *ia_iter.second << "\n\n";
ia_iter = equal_range( &ia[0], &ia[12], 21 );
cout << "equal_range result of search for "
<< "absent value 21:\n\t"
<< "*ia_iter.first: " << *ia_iter.first << "\t"
<< "*ia_iter.second: " << *ia_iter.second << "\n\n";
sort( ivec.begin(), ivec.end(), greater<int>() );
cout << "vector element sequence after sort:\n";
copy( ivec.begin(), ivec.end(), ofile ); cout << "\n\n";
typedef vector< int>::iterator iter_ivec;
pair< iter_ivec, iter_ivec > ivec_iter;
ivec_iter = equal_range( ivec.begin(), ivec.end(), 26,
greater<int>() );
cout << "equal_range result of search for value 26:\n\t"
<< "*ivec_iter.first: " << *ivec_iter.first << "\t"
<< "*ivec_iter.second: " << *ivec_iter.second
;
ivec_iter = equal_range( ivec.begin(), ivec.end(), 21,
greater<int>() );
cout << "equal_range result of search for "
<< "absent value 21:\n\t"
<< "*ivec_iter.first: " << *ivec_iter.first << "\t"
<< "*ivec_iter.second: " << *ivec_iter.second
;
}