STL中算法錦集(三)

文章目錄

• STL中算法錦集(三)
• • 一、< algorithm >
  • • 1.std::find_if
    • 2.std::find_if_not
    • 3.std::for_each
    • 4.std::generate
    • 5.std::generate_n
    • 6.std::includes
    • 7.std::inplace_merge
    • 8.std::is_heap
    • 9.std::is_heap_until
    • 10.std::is_partitioned

一、< algorithm >

1.std::find_if

• 原型：

template <class InputIterator, class UnaryPredicate>InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred);

• 參數：

• InputIterator first：區間的開始
• InputIterator last：區間的結束
• UnaryPredicate pred：自定義比較規則，可以是函數指針或者仿函數對象、lambda表達式

• 作用：[first,last)區間內找滿足pred條件的元素
• 返回值：返回第一個滿足pred條件的位置
• 實現：

template<class InputIterator, class UnaryPredicate>InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred) {while (first!=last) {if (pred(*first)) return first;++first;}return last; }

• 案例：

// find_if example #include <iostream> // std::cout #include <algorithm> // std::find_if #include <vector> // std::vectorbool IsOdd (int i) {return ((i%2)==1); }int main () {std::vector<int> myvector;myvector.push_back(10);myvector.push_back(25);myvector.push_back(40);myvector.push_back(55);std::vector<int>::iterator it = std::find_if (myvector.begin(), myvector.end(), IsOdd);std::cout << "The first odd value is " << *it << '\n';return 0; }Output: The first odd value is 25

2.std::find_if_not

• 原型：

template <class InputIterator, class UnaryPredicate>InputIterator find_if_not (InputIterator first, InputIterator last, UnaryPredicate pred);

• 參數：

• InputIterator first：區間的開始
• InputIterator last：區間的結束
• UnaryPredicate pred：自定義比較規則，可以是函數指針或者仿函數對象、lambda表達式

• 作用：[first,last)區間找滿足第一個不滿足pred條件元素的位置
• 返回值：返回第一個不滿足pred條件元素的位置
• 實現：

template<class InputIterator, class UnaryPredicate>InputIterator find_if_not (InputIterator first, InputIterator last, UnaryPredicate pred) {while (first!=last) {if (!pred(*first)) return first;++first;}return last; }

• 案例：

// find_if_not example #include <iostream> // std::cout #include <algorithm> // std::find_if_not #include <array> // std::arrayint main () {std::array<int,5> foo = {1,2,3,4,5};std::array<int,5>::iterator it =std::find_if_not (foo.begin(), foo.end(), [](int i){return i%2;} );std::cout << "The first even value is " << *it << '\n';return 0; }Output: The first even value is 2

3.std::for_each

• 原型：

template <class InputIterator, class Function>Function for_each (InputIterator first, InputIterator last, Function fn);

• 參數：

• InputIterator first：區間的開始
• InputIterator last：區間的結束
• Function fn：自定義動作，可以是函數指針或者仿函數對象、lambda表達式

• 作用：對[first,last)區間內的每個元素執行fn
• 返回值：返回每個元素執行的函數fn
• 實現：

template<class InputIterator, class Function>Function for_each(InputIterator first, InputIterator last, Function fn) {while (first!=last) {fn (*first);++first;}return fn; // or, since C++11: return move(fn); }

• 案例：

// for_each example #include <iostream> // std::cout #include <algorithm> // std::for_each #include <vector> // std::vectorvoid myfunction (int i) { // function:std::cout << ' ' << i; }struct myclass { // function object type:void operator() (int i) {std::cout << ' ' << i;} } myobject;int main () {std::vector<int> myvector;myvector.push_back(10);myvector.push_back(20);myvector.push_back(30);std::cout << "myvector contains:";for_each (myvector.begin(), myvector.end(), myfunction);std::cout << '\n';// or:std::cout << "myvector contains:";for_each (myvector.begin(), myvector.end(), myobject);std::cout << '\n';return 0; }Output: myvector contains: 10 20 30 myvector contains: 10 20 30

4.std::generate

• 原型：

template <class ForwardIterator, class Generator>void generate (ForwardIterator first, ForwardIterator last, Generator gen);

• 參數：

• ForwardIterator first：區間的開始
• ForwardIterator last：區間的結束
• Generator gen：自定義函數，可以是函數指針或者仿函數對象、lambda表達式

• 作用：把gen函數的執行結果賦值給[first,last)區間的每個位置
• 返回值：無返回值
• 實現：

template <class ForwardIterator, class Generator>void generate ( ForwardIterator first, ForwardIterator last, Generator gen ) {while (first != last) {*first = gen();++first;} }

• 案例：

// generate algorithm example #include <iostream> // std::cout #include <algorithm> // std::generate #include <vector> // std::vector #include <ctime> // std::time #include <cstdlib> // std::rand, std::srand// function generator: int RandomNumber () { return (std::rand()%100); }// class generator: struct c_unique {int current;c_unique() {current=0;}int operator()() {return ++current;} } UniqueNumber;int main () {std::srand ( unsigned ( std::time(0) ) );std::vector<int> myvector (8);std::generate (myvector.begin(), myvector.end(), RandomNumber);std::cout << "myvector contains:";for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)std::cout << ' ' << *it;std::cout << '\n';std::generate (myvector.begin(), myvector.end(), UniqueNumber);std::cout << "myvector contains:";for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)std::cout << ' ' << *it;std::cout << '\n';return 0; }A possible output: myvector contains: 57 87 76 66 85 54 17 15 myvector contains: 1 2 3 4 5 6 7 8

5.std::generate_n

• 原型：

//98 template <class OutputIterator, class Size, class Generator>void generate_n (OutputIterator first, Size n, Generator gen);//11 template <class OutputIterator, class Size, class Generator>OutputIterator generate_n (OutputIterator first, Size n, Generator gen);

• 參數：

• OutputIterator first：區間的開始
• Size n：個數
• Generator gen：自定義函數

• 作用：把gen函數的返回值作為[first,last)區間前n個元素的值
• 返回值：11返回最后一個成功賦值位置的下一個位置
• 實現：

template <class OutputIterator, class Size, class Generator>void generate_n ( OutputIterator first, Size n, Generator gen ) {while (n>0) {*first = gen();++first; --n;} }

• 案例：

// generate_n example #include <iostream> // std::cout #include <algorithm> // std::generate_nint current = 0; int UniqueNumber () { return ++current; }int main () {int myarray[9];std::generate_n (myarray, 9, UniqueNumber);std::cout << "myarray contains:";for (int i=0; i<9; ++i)std::cout << ' ' << myarray[i];std::cout << '\n';return 0; }A possible output: myarray contains: 1 2 3 4 5 6 7 8 9

6.std::includes

• 原型：

template <class InputIterator1, class InputIterator2>bool includes ( InputIterator1 first1, InputIterator1 last1,InputIterator2 first2, InputIterator2 last2 );template <class InputIterator1, class InputIterator2, class Compare>bool includes ( InputIterator1 first1, InputIterator1 last1,InputIterator2 first2, InputIterator2 last2, Compare comp );

• 參數：

• InputIterator1 first1：區間的開始
• InputIterator1 last1：區間的結束
• InputIterator2 first2：區間的開始
• InputIterator2 last2：區間的結束
• Compare comp：自定義比較規則
• 需要排序

• 作用：[first1,last1)區間是否全部包含[first2,last2)中的所有元素
• 返回值：是則返回true，反之返回false
• 實現：

template <class InputIterator1, class InputIterator2>bool includes (InputIterator1 first1, InputIterator1 last1,InputIterator2 first2, InputIterator2 last2) {while (first2!=last2) {if ( (first1==last1) || (*first2 < *first1) ) return false;if (!(*first1 < *first2)) ++first2;++first1;}return true; }

• 案例：

// includes algorithm example #include <iostream> // std::cout #include <algorithm> // std::includes, std::sortbool myfunction (int i, int j) { return i<j; }int main () {int container[] = {5,10,15,20,25,30,35,40,45,50};int continent[] = {40,30,20,10};std::sort (container,container+10);std::sort (continent,continent+4);// using default comparison:if ( std::includes(container,container+10,continent,continent+4) )std::cout << "container includes continent!\n";// using myfunction as comp:if ( std::includes(container,container+10,continent,continent+4, myfunction) )std::cout << "container includes continent!\n";return 0; }Output: container includes continent! container includes continent!

7.std::inplace_merge

• 原型：

template <class BidirectionalIterator>void inplace_merge (BidirectionalIterator first, BidirectionalIterator middle,BidirectionalIterator last);template <class BidirectionalIterator, class Compare>void inplace_merge (BidirectionalIterator first, BidirectionalIterator middle,BidirectionalIterator last, Compare comp);

• 參數：

• BidirectionalIterator first：區間的開始
• BidirectionalIterator middle：區間的中間位置，即分割線
• BidirectionalIterator last：區間的結束
• Compare comp：自定義比較規則
• [first,middle)區間和[middle,last)區間都需要有序，功能類似與排序，只不過是兩個有序小區間合并成一個大的有序區間

• 作用：把[first,middle)區間和[middle,last)區間合并并排序
• 返回值：無返回值
• 案例：

// inplace_merge example #include <iostream> // std::cout #include <algorithm> // std::inplace_merge, std::sort, std::copy #include <vector> // std::vectorint main () {int first[] = {5,10,15,20,25};int second[] = {50,40,30,20,10};std::vector<int> v(10);std::vector<int>::iterator it;//5 10 15 20 25std::sort (first,first+5);//10 20 30 40 50std::sort (second,second+5);//5 10 15 20 25 : 10 20 30 40 50it=std::copy (first, first+5, v.begin());std::copy (second,second+5,it);std::inplace_merge (v.begin(),v.begin()+5,v.end());std::cout << "The resulting vector contains:";for (it=v.begin(); it!=v.end(); ++it)std::cout << ' ' << *it;std::cout << '\n';return 0; }Output: The resulting vector contains: 5 10 10 15 20 20 25 30 40 50

8.std::is_heap

• 原型：

template <class RandomAccessIterator>bool is_heap (RandomAccessIterator first, RandomAccessIterator last);template <class RandomAccessIterator, class Compare>bool is_heap (RandomAccessIterator first, RandomAccessIterator last,Compare comp);

• 參數：

• RandomAccessIterator first：區間的開始
• RandomAccessIterator last：區間的結束
• Compare comp：自定義比較規則，可以是函數指針或者仿函數對象、lambda表達式

• 作用：判斷[first,last)區間元素是否構成一個堆
• 返回值：true代表構成一個堆，反之不構成堆
• 案例：

// is_heap example #include <iostream> // std::cout #include <algorithm> // std::is_heap, std::make_heap, std::pop_heap #include <vector> // std::vectorint main () {std::vector<int> foo {9,5,2,6,4,1,3,8,7};if (!std::is_heap(foo.begin(),foo.end()))std::make_heap(foo.begin(),foo.end());std::cout << "Popping out elements:";while (!foo.empty()) {std::pop_heap(foo.begin(),foo.end()); // moves largest element to backstd::cout << ' ' << foo.back(); // prints backfoo.pop_back(); // pops element out of container}std::cout << '\n';return 0; }Output: Popping out elements: 9 8 7 6 5 4 3 2 1

9.std::is_heap_until

• 原型：

template <class RandomAccessIterator>RandomAccessIterator is_heap_until (RandomAccessIterator first,RandomAccessIterator last);template <class RandomAccessIterator, class Compare>RandomAccessIterator is_heap_until (RandomAccessIterator first,RandomAccessIterator lastCompare comp);

• 參數：

• RandomAccessIterator first：區間的開始
• RandomAccessIterator last：區間的結束
• Compare comp：自定義比較規則，可以是函數指針或者仿函數對象、lambda表達式

• 作用：求[first,last)區間內第一個導致不滿足堆特性的元素位置
• 返回值：返回第一個導致不滿足堆特性的元素位置
• 案例：

#include <iostream> // std::cout #include <algorithm> // std::is_heap_until, std::sort, std::reverse #include <vector> // std::vectorint main () {std::vector<int> foo {2,6,9,3,8,4,5,1,7};std::sort(foo.begin(),foo.end());std::reverse(foo.begin(),foo.end());auto last = std::is_heap_until (foo.begin(),foo.end());std::cout << "The " << (last - foo.begin()) << " first elements are a valid heap:";for (auto it=foo.begin(); it!=last; ++it)std::cout << ' ' << *it;std::cout << '\n';return 0; }Most implementations consider a range sorted in reverse order a valid heap: Possible output: The 9 first elements are a valid heap: 9 8 7 6 5 4 3 2 1

10.std::is_partitioned

• 原型：

template <class InputIterator, class UnaryPredicate>bool is_partitioned (InputIterator first, InputIterator last, UnaryPredicate pred);

• 參數：

• InputIterator first：區間的開始
• InputIterator last：區間的結束
• UnaryPredicate pred：自定義比較規則，可以是函數指針或者仿函數對象、lambda表達式

• 作用：判斷[first,last)區間內的所有滿足pred條件的元素是否都在開始位置，且一旦出現不滿足pred的元素后，后面不能再出現滿足pred條件的元素
• 返回值：滿足條件返回true，反之返回false
• 實現：

template <class InputIterator, class UnaryPredicate>bool is_partitioned (InputIterator first, InputIterator last, UnaryPredicate pred) {while (first!=last && pred(*first)) {++first;}while (first!=last) {if (pred(*first)) return false;++first;}return true; }

• 案例：

// is_partitioned example #include <iostream> // std::cout #include <algorithm> // std::is_partitioned #include <array> // std::arraybool IsOdd (int i) { return (i%2)==1; }int main () {std::array<int,7> foo {1,2,3,4,5,6,7};// print contents:std::cout << "foo:"; for (int& x:foo) std::cout << ' ' << x;if ( std::is_partitioned(foo.begin(),foo.end(),IsOdd) )std::cout << " (partitioned)\n";elsestd::cout << " (not partitioned)\n";// partition array:std::partition (foo.begin(),foo.end(),IsOdd);// print contents again:std::cout << "foo:"; for (int& x:foo) std::cout << ' ' << x;if ( std::is_partitioned(foo.begin(),foo.end(),IsOdd) )std::cout << " (partitioned)\n";elsestd::cout << " (not partitioned)\n";return 0; }Possible output: foo: 1 2 3 4 5 6 7 (not partitioned) foo: 1 7 3 5 4 6 2 (partitioned)

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