C++ Algorithm unique()

2024年8月30日 | 5分钟阅读

C++ Algorithm unique() 函数用于转换序列，使得每个连续的重复元素都成为唯一的元素。

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内第一个元素位置的前向迭代器。

last：指向要扫描以删除重复项的范围内最后一个元素之后位置的前向迭代器。

pred：用户定义的谓词函数对象，定义了如果范围内两个元素被视为等效时应满足的条件。二元谓词接受两个参数，并在满足条件时返回 true，不满足时返回 false。0

返回值

一个前向迭代器，指向范围 [first, last) 的新末尾，该范围不包含连续的重复项。

复杂度

复杂度在范围 [first, last) 内呈线性关系：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

范围 [first, last) 中的对象被访问并可能被修改。

异常安全

如果 pred、元素比较、元素赋值或迭代器上的操作中的任何一个抛出异常，此函数将抛出异常。

注意：无效参数会导致未定义行为。

示例 1

让我们看一个简单的例子来演示 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

让我们看另一个例子

#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 ).

下一主题C++ 算法

C++ Algorithm unique()

语法

参数

返回值

复杂度

数据竞争

异常安全

注意：无效参数会导致未定义行为。

示例 1

示例 2

示例 3

示例 4

示例 5

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C++ Algorithm unique()

语法

参数

返回值

复杂度

数据竞争

异常安全

注意：无效参数会导致未定义行为。

示例 1

示例 2

示例 3

示例 4

示例 5

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