總所周知,C++ STL中有個頭文件,名為algorithm,即算法的意思。
The headerdefines a collection of functions especially designed to be used on ranges of elements.
所以,要八一八這個頭文件中C++11新增的幾個算法,今天主要描述的幾個算法不改變容器中元素的順序。
這裡還要啰嗦一句,使用stl算法時,如果與lambda表達式組合使用,那麼代碼會更加簡潔。
find_if_not
該算法在之前介紹過,請參閱博客《實戰c++中的vector系列–vector應用之STL的find、find_if、find_end、find_first_of、find_if_not(C++11)》。
all_of
原型:
template
bool all_of (InputIterator first, InputIterator last, UnaryPredicate pred);
作用:
Test condition on all elements in range
Returns true if pred returns true for all the elements in the range [first,last) or if the range is empty, and false otherwise.
檢測區間[first, last)中是否所有的元素都滿足一元判斷表達式pred。所有的元素都滿足條件返回true,否則返回false.
應用:
#include // std::cout
#include // std::all_of
#include // std::array
int main () {
std::array foo = {3,5,7,11,13,17,19,23};
if ( std::all_of(foo.begin(), foo.end(), [](int i){return i%2;}) )
std::cout << "All the elements are odd numbers.\n";
return 0;
}
//輸出:
All the elements are odd numbers.
any_of
原型:
template
bool any_of (InputIterator first, InputIterator last, UnaryPredicate pred);
作用:
Test if any element in range fulfills condition
Returns true if pred returns true for any of the elements in the range [first,last), and false otherwise.
應用:
#include // std::cout
#include // std::any_of
#include // std::array
int main () {
std::array foo = {0,1,-1,3,-3,5,-5};
if ( std::any_of(foo.begin(), foo.end(), [](int i){return i<0;}) )
std::cout << "There are negative elements in the range.\n";
return 0;
}
//輸出:
There are negative elements in the range.
none_of
原型:
template
bool none_of (InputIterator first, InputIterator last, UnaryPredicate pred);
作用:
Returns true if pred returns false for all the elements in the range [first,last) or if the range is empty, and false otherwise.
應用:
#include // std::cout
#include // std::none_of
#include // std::array
int main () {
std::array foo = {1,2,4,8,16,32,64,128};
if ( std::none_of(foo.begin(), foo.end(), [](int i){return i<0;}) )
std::cout << "There are no negative elements in the range.\n";
return 0;
}
//輸出:
There are no negative elements in the range.
is_permutation
permutation 名詞 排列 、交換等意思。
該函數是用來判斷兩個序列是否為同一元素集的不同排列!
該函數使用operator==或者是pred來判斷兩個元素是否是相等的。
原型:
template
bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2);
template
bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, BinaryPredicate pred);
作用:
Test whether range is permutation of another
Compares the elements in the range [first1,last1) with those in the range beginning at first2, and returns true if all of the elements in both ranges match, even in a different order.
應用:
#include // std::cout
#include // std::is_permutation
#include // std::array
int main () {
std::array foo = {1,2,3,4,5};
std::array bar = {3,1,4,5,2};
if ( std::is_permutation (foo.begin(), foo.end(), bar.begin()) )
std::cout << "foo and bar contain the same elements.\n";
return 0;
}
//輸出:
foo and bar contain the same elements.
這裡需要注意的是,你不能突發奇想,比如用大於號或是小於號進行比較,你只能這樣:
The elements are compared using operator== (or pred)