C++ unique()
C++算法unique()
C++算法 unique()函数用于转换序列，使每个重复的连续元素成为一个独特的元素。
第一个版本使用operator ==比较元素，第二个版本使用给定的二进制谓词pred。
语法
equality (1) template <class ForwardIterator>
ForwardIterator unique (ForwardIterator first, ForwardIterator last);
predicate (2) template <class ForwardIterator, class BinaryPredicate>
ForwardIterator unique (ForwardIterator first, ForwardIterator last,
BinaryPredicate pred);
参数
first: 一个正向迭代器，指向要扫描以进行重复删除的范围内第一个元素的位置。
last: 前向迭代器，指向要扫描的重复范围中距离最终元素一个位置的位置。
pred : 用户定义的谓词函数对象，该对象定义了将范围中的两个元素视为等效时要满足的条件。二进制谓词返回两个参数，满足时返回true，不满足时返回false。 0
返回值
一个正向迭代器，它指向不包含连续重复项的范围的新末端(第一个，最后一个)。
复杂度
复杂度在[first，last)范围内是线性的: 比较每对连续的元素，并对其中一些元素执行赋值操作。
数据竞争
可以访问并可能修改[first，last)范围内的对象。
异常安全
如果pred，元素比较，元素分配或迭代器上的任何操作抛出异常，则此函数将引发异常。
注意: 无效的参数会导致未定义的行为。
示例1
让我们看一个简单的示例来演示unique()的用法:
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cctype>
using namespace std;
int main()
{
// remove duplicate elements
vector<int> v{1,2,3,1,2,3,3,4,5,4,5,6,7};
sort(v.begin(), v.end());
auto last = unique(v.begin(), v.end());
// v now holds {1 2 3 4 5 6 7 x x x x x x}, where 'x' is indeterminate
v.erase(last, v.end());
for (int i : v)
cout << i << " ";
cout << "\n";
return 0;
}
输出:
示例2
让我们看另一个简单的示例:
#include <iostream> // std::cout
#include <algorithm> // std::unique, std::distance
#include <vector> // std::vector
using namespace std;
bool myfunction (int i, int j) {
return (i==j);
}
int main () {
int myints[] = {10,20,20,20,30,30,20,20,10}; // 10 20 20 20 30 30 20 20 10
vector<int> myvector (myints,myints+9);
// using default comparison:
vector<int>::iterator it;
it = unique (myvector.begin(), myvector.end()); // 10 20 30 20 10 ? ? ? ?
// ^
myvector.resize( distance(myvector.begin(),it) ); // 10 20 30 20 10
// using predicate comparison:
unique (myvector.begin(), myvector.end(), myfunction); // (no changes)
// print out content:
std::cout << "myvector contains:";
for (it=myvector.begin(); it!=myvector.end(); ++it)
cout << ' ' << *it;
cout << '\n';
return 0;
}
输出:
myvector contains: 10 20 30 20 10
示例3
让我们看另一个简单的示例:
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
void print(const char* tag, const vector<int>& v) {
cout << tag << " : ";
bool first = true;
for (int x : v) {
if (first) {
first = false;
}
else {
cout << ',';
}
cout << x;
}
cout << endl;
}
int main() {
{
vector<int> v = { 2,5,3,3,1,2,4,2,1,1,4,4,3,3,3 };
decltype(v)::iterator result = unique(v.begin(), v.end());
v.erase(result, v.end());
print("unsorted unique", v);
}
{
vector<int> v = { 2,5,3,3,1,2,4,2,1,1,4,4,3,3,3 };
sort(v.begin(), v.end());
decltype(v)::iterator result = unique(v.begin(), v.end());
v.erase(result, v.end());
print("sorted unique", v);
}
}
输出:
unsorted unique : 2,5,3,1,2,4,2,1,4,3
sorted unique : 1,2,3,4,5
示例4
让我们看另一个简单的示例:
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cctype>
using namespace std;
int main()
{
// remove duplicate elements (normal use)
vector<int> v{1,2,3,1,2,3,3,4,5,4,5,6,7};
sort(v.begin(), v.end()); // 1 1 2 2 3 3 3 4 4 5 5 6 7
auto last = unique(v.begin(), v.end());
// v now holds {1 2 3 4 5 6 7 x x x x x x}, where 'x' is indeterminate
v.erase(last, v.end());
for (int i : v)
cout << i << " ";
cout << "\n";
// remove consecutive spaces
string s = "wanna go to space?";
auto end = unique(s.begin(), s.end(), [](char l, char r){
return isspace(l) && isspace(r) && l == r;
});
// s now holds "wanna go to space?xxxxxxxx", where 'x' is indeterminate
cout << string(s.begin(), end) << '\n';
}
输出:
1 2 3 4 5 6 7
wanna go to space?
示例5
让我们看看另一个示例:
#include <vector>
#include <algorithm>
#include <functional>
#include <iostream>
#include <ostream>
using namespace std;
// return whether modulus of elem1 is equal to modulus of elem2
bool mod_equal ( int elem1, int elem2 )
{
if ( elem1 < 0 )
elem1 =-elem1;
if ( elem2 < 0 )
elem2 =-elem2;
return elem1 == elem2;
};
int main( )
{
vector <int> v1;
vector <int>::iterator v1_Iter1, v1_Iter2, v1_Iter3,
v1_NewEnd1, v1_NewEnd2, v1_NewEnd3;
int i;
for ( i = 0 ; i <= 3 ; i++ )
{
v1.push_back( 5 );
v1.push_back(-5 );
}
int ii;
for ( ii = 0 ; ii <= 3 ; ii++ )
{
v1.push_back( 4 );
}
v1.push_back( 7 );
cout << "Vector v1 is ( " ;
for ( v1_Iter1 = v1.begin( ) ; v1_Iter1 != v1.end( ) ; v1_Iter1++ )
cout << *v1_Iter1 << " ";
cout << ")." << endl;
// Remove consecutive duplicates
v1_NewEnd1 = unique ( v1.begin ( ) , v1.end ( ) );
cout << "Removing adjacent duplicates from vector v1 gives\n ( " ;
for ( v1_Iter1 = v1.begin( ) ; v1_Iter1 != v1_NewEnd1 ; v1_Iter1++ )
cout << *v1_Iter1 << " ";
cout << ")." << endl;
// Remove consecutive duplicates under the binary prediate mod_equals
v1_NewEnd2 = unique ( v1.begin ( ) , v1_NewEnd1 , mod_equal );
cout << "Removing adjacent duplicates from vector v1 under the\n "
<< " binary predicate mod_equal gives\n ( " ;
for ( v1_Iter2 = v1.begin( ) ; v1_Iter2 != v1_NewEnd2 ; v1_Iter2++ )
cout << *v1_Iter2 << " ";
cout << ")." << endl;
// Remove elements if preceded by an element that was greater
v1_NewEnd3 = unique ( v1.begin ( ) , v1_NewEnd2, greater<int>( ) );
cout << "Removing adjacent elements satisfying the binary\n "
<< " predicate mod_equal from vector v1 gives ( " ;
for ( v1_Iter3 = v1.begin( ) ; v1_Iter3 != v1_NewEnd3 ; v1_Iter3++ )
cout << *v1_Iter3 << " ";
cout << ")." << endl;
return 0;
}
输出:
Vector v1 is ( 5-5 5-5 5-5 5-5 4 4 4 4 7 ).
Removing adjacent duplicates from vector v1 gives
( 5-5 5-5 5-5 5-5 4 7 ).
Removing adjacent duplicates from vector v1 under the
binary predicate mod_equal gives
( 5 4 7 ).
Removing adjacent elements satisfying the binary
predicate mod_equal from vector v1 gives ( 5 7 ).
