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partition

Classifies elements in a range into two disjoint sets, with those elements satisfying a unary predicate preceding those that fail to satisfy it.

template<class BidirectionalIterator, class Predicate>
   BidirectionalIterator partition(
      BidirectionalIterator _First, 
      BidirectionalIterator _Last, 
      BinaryPredicate _Comp
   );

Parameters

_First
A bidirectional iterator addressing the position of the first element in the range to be partitioned.
_Last
A bidirectional iterator addressing the position one past the final element in the range to be partitioned.
_Comp
User-defined predicate function object that defines the condition to be satisfied if an element is to be classified. A predicate takes a single argument and returns true or false.

Return Value

A bidirectional iterator addressing the position of the first element in the range to not satisfy the predicate condition.

Remarks

The range referenced must be valid; all pointers must be dereferenceable and within the sequence the last position is reachable from the first by incrementation.

Elements a and b are equivalent, but not necessarily equal, if both Pr (a, b) is false and Pr (b, a) if false, where Pr is the parameter-specified predicate. The partition algorithm is not stable and does not guarantee that the relative ordering of equivalent elements will be preserved. The algorithm stable_ partition does preserve this original ordering.

The complexity is linear: there are (_Last – _First) applications of _Comp and at most (_Last – _First)/2 swaps.

Example

// alg_partition.cpp
// compile with: /EHsc
#include <vector>
#include <algorithm>
#include <iostream>

bool greater5 ( int value )
{
   return value >5;
}

int main( ) {
   using namespace std;
   vector <int> v1, v2;
   vector <int>::iterator Iter1, Iter2;

   int i;
   for ( i = 0 ; i <= 10 ; i++ )
   {
      v1.push_back( i );
   }
   random_shuffle( v1.begin( ), v1.end( ) );

   cout << "Vector v1 is ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;

   // Partition the range with predicate greater10
   partition ( v1.begin( ), v1.end( ), greater5 );
   cout << "The partitioned set of elements in v1 is: ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;
}

Output

Vector v1 is ( 10 1 9 2 0 5 7 3 4 6 8 ).
The partitioned set of elements in v1 is: ( 10 8 9 6 7 5 0 3 4 2 1 ).

See Also

<algorithm> Members | partition Sample

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