C++语法基础--泛型算法（generic algorithm)--对容器排序的算法sort(),stable_sort(),unique()
2013-07-12 11:12
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1.sort
Sorts the elements in the range [first,last) into ascending order.
The elements are compared using operator< for the first version, and comp for the second.
Equivalent elements are not guaranteed to keep their original relative order
原型：
default：
template <class RandomAccessIterator>
void sort (RandomAccessIterator first, RandomAccessIterator last);
custom：
template <class RandomAccessIterator, class Compare>
void sort (RandomAccessIterator first, RandomAccessIterator last, Compare comp);
解析：
first, last：
Random-access iterators to the initial and final positions of the sequence to be sorted.
comp ：
Binary function that accepts two elements in the range as arguments, and returns a value convertible to bool.
Example:
int main ()
{
int myints[] = {11,2,10,9,3,7,13,6};
vector<int> myvector (myints, myints+8);
// using default comparison (operator <):
sort (myvector.begin(), myvector.begin()+4); //(2,9,10,11),3,7,13,6
// using function as comp
sort (myvector.begin()+4, myvector.end(), myfunction); // 2,9,10,11,(3,6,7,13)
return 0;
}
2.stable_sort
同sort(),但stable_sort是稳定的算法，即排序后容器内相等元素相对位置不变
（例：假设排序前相等元素a1在a2前面，排序后a1还是在a2前面）
3.unique
Removes all but the first element from every consecutive(连续的) group of equivalent elements in the range [first,last).
The function uses operator== to compare the pairs of elements (or pred, in version (2)).
原型：
equality ：
template <class ForwardIterator>
ForwardIterator unique (ForwardIterator first, ForwardIterator last);
predicate ：
template <class ForwardIterator, class BinaryPredicate>
ForwardIterator unique (ForwardIterator first, ForwardIterator last,
BinaryPredicate pred);
解析：
first, last：
Forward iterators to the initial and final positions of the sequence of move-assignable elements.
pred ：
Binary function that accepts two elements in the range as argument, and returns a value convertible to bool.
该算法等效于：
template <class ForwardIterator>
ForwardIterator unique (ForwardIterator first, ForwardIterator last)
{
if (first==last) return last;
ForwardIterator result = first;
while (++first != last)
{
if (!(*result == *first)) // or: if (!pred(*result,*first)) for version (2)
*(++result)=*first;
}
return ++result;
}
Tips:
从上面的等效算法中可以看出：unique并没有删除容器内的元素，一般情况下，unique会搭配sort（）函数先排序
，再用容器的resize()函数重新调整大小（截断容器后面的元素），以达到保留容器内唯一元素的目的。
Example:
bool myfunction (int i, int j) {
return (i==j);
}
int main () {
int myints[] = {1,1,1,2,2,3,3,1,2,3};
std::vector<int> myvector (myints,myints+10);
sort(myvector.begin(),myvector.end());//1,1,1,1,2,2,2,3,3,3
// using default comparison:
vector<int>::iterator it;
it=unique (myvector.begin(), myvector.end());
//1,2,3,1,2,2,2,3,3,3
myvector.resize(it-myvector.begin());//1,2,3
// myvector contains:
for (it=myvector.begin(); it!=myvector.end(); ++it)
{
cout << ' ' << *it; //1,2,3
}
// using predicate comparison:
unique (myvector.begin(), myvector.end(), myfunction); // (no changes)
return 0;
}
Sorts the elements in the range [first,last) into ascending order.
The elements are compared using operator< for the first version, and comp for the second.
Equivalent elements are not guaranteed to keep their original relative order
原型：
default：
template <class RandomAccessIterator>
void sort (RandomAccessIterator first, RandomAccessIterator last);
custom：
template <class RandomAccessIterator, class Compare>
void sort (RandomAccessIterator first, RandomAccessIterator last, Compare comp);
解析：
first, last：
Random-access iterators to the initial and final positions of the sequence to be sorted.
comp ：
Binary function that accepts two elements in the range as arguments, and returns a value convertible to bool.
Example:
int main ()
{
int myints[] = {11,2,10,9,3,7,13,6};
vector<int> myvector (myints, myints+8);
// using default comparison (operator <):
sort (myvector.begin(), myvector.begin()+4); //(2,9,10,11),3,7,13,6
// using function as comp
sort (myvector.begin()+4, myvector.end(), myfunction); // 2,9,10,11,(3,6,7,13)
return 0;
}
2.stable_sort
同sort(),但stable_sort是稳定的算法，即排序后容器内相等元素相对位置不变
（例：假设排序前相等元素a1在a2前面，排序后a1还是在a2前面）
3.unique
Removes all but the first element from every consecutive(连续的) group of equivalent elements in the range [first,last).
The function uses operator== to compare the pairs of elements (or pred, in version (2)).
原型：
equality ：
template <class ForwardIterator>
ForwardIterator unique (ForwardIterator first, ForwardIterator last);
predicate ：
template <class ForwardIterator, class BinaryPredicate>
ForwardIterator unique (ForwardIterator first, ForwardIterator last,
BinaryPredicate pred);
解析：
first, last：
Forward iterators to the initial and final positions of the sequence of move-assignable elements.
pred ：
Binary function that accepts two elements in the range as argument, and returns a value convertible to bool.
该算法等效于：
template <class ForwardIterator>
ForwardIterator unique (ForwardIterator first, ForwardIterator last)
{
if (first==last) return last;
ForwardIterator result = first;
while (++first != last)
{
if (!(*result == *first)) // or: if (!pred(*result,*first)) for version (2)
*(++result)=*first;
}
return ++result;
}
Tips:
从上面的等效算法中可以看出：unique并没有删除容器内的元素，一般情况下，unique会搭配sort（）函数先排序
，再用容器的resize()函数重新调整大小（截断容器后面的元素），以达到保留容器内唯一元素的目的。
Example:
bool myfunction (int i, int j) {
return (i==j);
}
int main () {
int myints[] = {1,1,1,2,2,3,3,1,2,3};
std::vector<int> myvector (myints,myints+10);
sort(myvector.begin(),myvector.end());//1,1,1,1,2,2,2,3,3,3
// using default comparison:
vector<int>::iterator it;
it=unique (myvector.begin(), myvector.end());
//1,2,3,1,2,2,2,3,3,3
myvector.resize(it-myvector.begin());//1,2,3
// myvector contains:
for (it=myvector.begin(); it!=myvector.end(); ++it)
{
cout << ' ' << *it; //1,2,3
}
// using predicate comparison:
unique (myvector.begin(), myvector.end(), myfunction); // (no changes)
return 0;
}
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