极客笔记C++ 算法 unique()函数
C++ 算法 unique() 函数用于将序列转换成每个重复连续元素变成一个独特元素的形式。
第一个版本使用 operator== 来比较元素，第二个版本使用给定的二元谓词 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 : 指向要扫描以删除重复项的范围中第一个元素的前向迭代器。
last : 指向要扫描以删除重复项的范围中最后一个元素之后位置的前向迭代器。
pred :一个用户自定义的谓词函数对象，用于定义如果范围中的两个元素被视为相等，则应满足的条件。二元谓词返回两个参数，并在满足时返回true，在不满足时返回false。
返回值
一个前向迭代器，指向不包含连续重复项的范围[first，last)的新结尾。
复杂度
在范围[first，last)中的复杂度为线性 ：比较每一对相邻元素，并在其中一些元素上执行赋值操作。
数据竞争
范围[first，last)中的对象被访问并可能被修改。
异常安全性
如果pred、元素比较、元素赋值或迭代器操作中的任何一个抛出异常，此函数会抛出异常。
注意：无效的参数会导致未定义行为。
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：
1 2 3 4 5 6 7
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
来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 ).