Brings the elements into a random order
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Definition
The random_shuffle() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.
Interface
#include <algorithm>
template < class RandomAccessIterator >
void random_shuffle(
RandomAccessIterator first,
RandomAccessIterator last
);
template < class RandomAccessIterator, class RandomNumberGenerator >
void random_shuffle(
RandomAccessIterator first,
RandomAccessIterator last,
RandomNumberGenerator& rand
);
Parameters:
| Parameter | Description |
| first | A random-access iterator addressing the position of the first element in the range to be rearranged |
| last | A random-access iterator addressing the position one past the final element in the range to be rearranged |
| rand | A special function object called a random number generator |
Description
Random_shuffle function reorders the elements of a range by putting them at random places.
The first version uses an internal random number generator, and the second uses a Random Number Generator, a special kind of function object, that is explicitly passed as an argument.
Return Value
None.
Complexity
The complexity is linear; performs as many calls to swap as the length of the range [first,last) - 1.
References
Example 1
ProblemThis program illustrates the use of the STL random_shuffle() algorithm (default version) to randomize the order of values in a vector of integers.
Workings#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
int a[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
vector<int> v(a, a+10);
cout <<"\nHere are the values in the vector:\n";
for (vector<int>::size_type i=0; i<v.size(); i++)
cout <<v.at(i)<<" ";
cout << "\nNow we randomize the order of the values.";
random_shuffle(v.begin(), v.end());
cout <<"\nHere are the revised contents of the vector:\n";
for (vector<int>::size_type i=0; i<v.size(); i++)
cout <<v.at(i)<<" ";
return 0;
}
SolutionOutput:
Here are the values in the vector:
1 2 3 4 5 6 7 8 9 10
Now we randomize the order of the values.
Here are the revised contents of the vector:
9 2 10 3 1 6 8 4 5 7
Example 2
ProblemThis program illustrates the use of the STL random_shuffle() algorithm (extended version) to randomize the order of values in a vector of integers, this time with the aid of a programmer-supplied pseudorandom number generator.
Workings#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
class MyRandom
{
public:
ptrdiff_t operator() (ptrdiff_t max)
{
double tmp;
tmp = static_cast<double>(rand())
/ static_cast<double>(RAND_MAX);
return static_cast<ptrdiff_t>(tmp * max);
}
};
int main()
{
int a[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
vector<int> v(a, a+10);
cout <<"\nHere are the values in the vector:\n";
for (vector<int>::size_type i=0; i<v.size(); i++)
cout <<v.at(i)<<" ";
cout <<"\nNow we randomize the order of the values.";
MyRandom generator;
random_shuffle(v.begin(), v.end(), generator);
cout <<"\nHere are the revised contents of the vector:\n";
for (vector<int>::size_type i=0; i<v.size(); i++)
cout <<v.at(i)<<" ";
return 0;
}
SolutionOutput:
Here are the values in the vector:
1 2 3 4 5 6 7 8 9 10
Now we randomize the order of the values.
Here are the revised contents of the vector:
4 3 8 7 5 2 6 1 10 9
See Also
