【C++標准庫】STL算法

使用C++標准庫的算法，需包含頭文件<algorithm>

STL算法用於處理一個或多個iterator區間，第一個區間通常以起點和終點表示，其他區間則多數情況下只需提供起點足矣，其終點可以根據第一區間的元素數量推導出來。調用者需保證區間的有效性。STL算法命名時，引入了兩種特殊的后綴：

STL算法分類

• 非更易型算法（nomodifying algorithm）
• 更易型算法（modifying algorithm）
• 移除型算法（removing algorithm）
• 變序型算法（mutating algorithm）
• 排序算法（sorting algorithm）
• 已排序區間算法（sorted-range algorithm）
• 數值算法（numeric algorithm）

 非更易型算法

更易型算法

/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference, 2nd Edition"
* by Nicolai M. Josuttis, Addison-Wesley, 2012
*
* (C) Copyright Nicolai M. Josuttis 2012.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include "algostuff.hpp"
using namespace std;

int main()
{
    vector<string> coll1 = { "Hello", "this", "is", "an", "example" };
    list<string> coll2;

    // copy elements of coll1 into coll2
    // - use back inserter to insert instead of overwrite
    // - use copy() because the elements in coll1 are used again
    copy(coll1.cbegin(), coll1.cend(),         // source range
        back_inserter(coll2));                // destination range

    // print elements of coll2
    // - copy elements to cout using an ostream iterator
    // - use move() because these elements in coll2 are not used again
    move(coll2.cbegin(), coll2.cend(),         // source range
        ostream_iterator<string>(cout, " "));  // destination range
    cout << endl;

    // copy elements of coll1 into coll2 in reverse order
    // - now overwriting (coll2.size() still fits)
    // - use move() because the elements in coll1 are not used again
    move(coll1.crbegin(), coll1.crend(),       // source range
        coll2.begin());                       // destination range

    // print elements of coll2 again
    // - use move() because the elements in coll2 are not used again
    move(coll2.cbegin(), coll2.cend(),         // source range
    ostream_iterator<string>(cout, " "));  // destination range
    cout << endl;
}

#include "algostuff.hpp"
using namespace std;

int main()
{
    array<int, 10> coll;
    iota(coll.begin(), coll.end(), 42);
    PRINT_ELEMENTS(coll,"coll:");  //42 43 44 45 46 47 48 49 50 51
    return 0;
}

#include "algostuff.hpp"
using namespace std;
using namespace std::placeholders;

int main()
{
    list<int> coll;
    INSERT_ELEMENTS(coll, 2, 6);
    INSERT_ELEMENTS(coll, 4, 9);
    PRINT_ELEMENTS(coll);

    //print all elements with 5 replaced with 55
    replace_copy(coll.cbegin(), coll.cend(), ostream_iterator<int>(cout, " "), 5, 55);
    cout << endl;
    //print all elements with a value less than 5 replaced with 42
    replace_copy_if(coll.cbegin(), coll.cend(), ostream_iterator<int>(cout, " "), bind(less<int>(), _1, 5), 42);
    cout << endl;
    //print all elements while each odd value replaced with 0
    replace_copy_if(coll.cbegin(), coll.cend(), ostream_iterator<int>(cout, " "), [](int elem) {return elem % 2 == 1;}, 0);
    cout << endl;
    return 0;
}

移除型算法

移除型算法只是從“邏輯上”移除元素，其手段是將不應移除的元素往前覆蓋應被移除的元素，因此其並未改變操作區間內元素的個數，而是返回邏輯上新終點的位置。

變序型算法

#include "algostuff.hpp"
using namespace std;
using namespace std::placeholders;

int main()
{
    vector<int> coll = { 1,6,33,7,22,4,11,33,2,7,0,42,5 };
    PRINT_ELEMENTS(coll, "coll:");
    vector<int> evenColl;
    vector<int> oddColl;
    //copy all elements accordingly into even and odd elements
    partition_copy(coll.cbegin(), coll.cend(),back_inserter(evenColl),back_inserter(oddColl),[](int elem) {return elem % 2 == 0;});
    PRINT_ELEMENTS(evenColl, "evenColl:");
    PRINT_ELEMENTS(oddColl, "oddColl:");
    return 0;
}

排序算法

已排序區間算法

數值算法

 使用數值算法時，需包含頭文件<numeric>