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Changes the order of the elements so that elements that match a criterion are at the front
Key Facts
Gyroscopic Couple: The rate of change of angular momentum (= Moment of Inertia.
= Angular velocity
= Angular velocity of precession.
Blaise Pascal (1623-1662) was a French mathematician, physicist, inventor, writer and Catholic philosopher.
Leonhard Euler (1707-1783) was a pioneering Swiss mathematician and physicist.
Definition
The partition() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.Interface
#include <algorithm> template < class BidirectionalIterator, class Predicate > BidirectionalIterator partition( BidirectionalIterator first, BidirectionalIterator last, Predicate comp );Parameters:
| Parameter | Description |
|---|---|
| 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 |
Description
Partition function cuts a range in two parts : all elements in the first part satisfy a predicate and elements in the second part doesn't. After a call to partition, relative order between elements may be changed.Complexity
The complexity is linear; performslast - first applications of pred and at most (last - first)/2 swaps.References
Example:
Example - partition algorithm
Problem
This program illustrates the use of the STL partition() algorithm to partition the integer values in a vector of integers into two groups: those that are divisible by 3, and those that are not.
Workings
#include <iostream> #include <vector> #include <algorithm> using namespace std; /* Determines if an integer is divisible by 3. n contains an integer Returns true if n is divisible by 3, and otherwise false. */ bool isDivisibleByThree ( int n //in ) { return (n%3 == 0); } int main() { int a[] ={11, 7, 9, 4, 8, 12, 2, 5, 3, 10, 1, 6}; vector<int> v(a, a+12); cout <<"\nHere are the contents of the vector:\n"; for (vector<int>::size_type i=0; i<v.size(); i++) cout <<v.at(i)<<" "; vector<int>::iterator p = partition(v.begin(), v.end(), isDivisibleByThree); cout <<"\nAnd here are the contents of the partitioned vector:\n"; for (vector<int>::size_type i=0; i<v.size(); i++) cout <<v.at(i)<<" "; cout <<"\nThe iterator p returned by the algorithm points to "; if (p == v.end()) cout <<"\nthe end of the ouput container."; else cout <<"the value "<<*p<<"."; return 0; }
Solution
Output:
Here are the contents of the vector:
11 7 9 4 8 12 2 5 3 10 1 6 And here are the contents of the partitioned vector:
6 3 9 12 8 4 2 5 7 10 1 11 The iterator p returned by the algorithm points to the value 8.
11 7 9 4 8 12 2 5 3 10 1 6 And here are the contents of the partitioned vector:
6 3 9 12 8 4 2 5 7 10 1 11 The iterator p returned by the algorithm points to the value 8.
References