Apr 23, 2017 We have discussed map in C STL and multimap in C STL.The default behavior of these data structures is to store elements in ascending order. How to ensure reverse order or descending order when inserting elements in map and multimap. How to ensure reverse order or descending order when inserting elements in map and multimap. The idea is to greater function when an instance of map/multimap. Descending order in map: A map stores key value pairs. A self-balancing-BST (typically Red-Black tree) is used to implement it.
< cpp | algorithm
C++Language | ||||
Standard Library Headers | ||||
Freestanding and hosted implementations | ||||
Named requirements | ||||
Language support library | ||||
Concepts library(C++20) | ||||
Diagnostics library | ||||
Utilities library | ||||
Strings library | ||||
Containers library | ||||
Iterators library | ||||
Ranges library(C++20) | ||||
Algorithms library | ||||
Numerics library | ||||
Input/output library | ||||
Localizations library | ||||
Regular expressions library(C++11) | ||||
Atomic operations library(C++11) | ||||
Thread support library(C++11) | ||||
Filesystem library(C++17) | ||||
Technical Specifications |
Constrained algorithms and algorithms on ranges (C++20) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Concepts and utilities: std::sortable , std::projected , .. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Constrained algorithms: std::ranges::copy , std::ranges::sort , .. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Execution policies (C++17) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Non-modifying sequence operations | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Operations on uninitialized storage | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Partitioning operations | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Sorting operations | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Binary search operations | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Set operations (on sorted ranges) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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C library |
Defined in header <algorithm> | ||
(1) | ||
template<class ForwardIt, class Generator > void generate( ForwardIt first, ForwardIt last, Generator g ); | (until C++20) | |
template<class ForwardIt, class Generator > constexprvoid generate( ForwardIt first, ForwardIt last, Generator g ); | (since C++20) | |
template<class ExecutionPolicy, class ForwardIt, class Generator > void generate( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Generator g ); | (2) | (since C++17) |
1) Assigns each element in range
[first, last)
a value generated by the given function object g
.2) Same as (1), but executed according to
policy
. This overload does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>(until C++20)std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>(since C++20) is true.[edit]Parameters
[edit]Return value
(none)
[edit]Complexity
Exactly std::distance(first, last) invocations of
g()
and assignments.[edit]Exceptions
The overload with a template parameter named
ExecutionPolicy
reports errors as follows:- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy
is one of the standard policies, std::terminate is called. For any otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
Golang Sort Int Array
[edit]Possible implementation
[edit]Example
Output:
[edit]See also
copy-assigns the given value to every element in a range (function template)[edit] | |
assigns the results of successive function calls to N elements in a range (function template)[edit] | |
(C++11) | fills a range with successive increments of the starting value (function template)[edit] |
Retrieved from 'https://en.cppreference.com/mwiki/index.php?title=cpp/algorithm/generate&oldid=117767'
One mathematical function in C programming that’s relatively easy to grasp is the rand() function. It generates random numbers. Though that may seem silly, it’s the basis for just about every computer game ever invented. Random numbers are a big deal in programming.
A computer cannot generate truly random numbers. Instead, it produces what are known as pseudo–random numbers. That’s because conditions inside the computer can be replicated. Therefore, serious mathematicians scoff that any value a computer calls random isn’t a truly random number. Can you hear them scoffing?
How to generate random numbers
The rand() function is the simplest of C’s random-number functions. It requires the stdlib.h header file, and it coughs up an int value that’s supposedly random. Now, That’s Random demonstrates sample code.
NOW, THAT’S RANDOM
Now, That’s Random uses a nested for loop to display 100 random values. The rand() function in Line 13 generates the values. The printf() function in Line 14 displays the values by using the %d conversion character, which displays int values.
Exercise 1: Create a new project by using the source code shown in Now, That’s Random. Build and run to behold 100 random values.
Exercise 2: Modify the code so that all the values displayed are in the range 0 through 20.
C Generate Sort Key By Int Number
Here’s a hint for Now, That’s Random: Use the modulus assignment operator to limit the range of the random numbers. The format looks like this:
r is the number returned from the rand() function. %= is the modulus assignment operator. n is the range limit, plus 1. After the preceding statement, values returned are in the range 0 through n-1. So if you want to generate values between 1 and 100, you would use this formula:
How to increase the randomness of numbersin C programming
Just to give some credit to the snooty mathematicians who claim that computers generate pseudo-random numbers, run the program you generated from Exercise 2. Observe the output. Run the program again. See anything familiar?
The rand() function is good at generating a slew of random values, but they’re predictable values. To make the output less predictable, you need to seed the random-number generator. That’s done by using the srand() function.
Like the rand() function, the srand() function requires the stdlib.h header, shown at Line 2 in Even More Randomness. The function requires an unsigned int value, seed, which is declared at Line 6. The scanf() function at Line 10 reads in the unsigned value by using the %u placeholder. Then the srand() function uses the seed value in Line 11.
EVEN MORE RANDOMNESS
The rand() function is used at Line 16, although the results are now based on the seed, which is set when the program runs.
Exercise 3: Create a new project using the source code shown in Even More Randomness. Build it. Run the program a few times, trying different seed values. The output is different every time.
Alas, the random values that are generated are still predictable when you type the same seed number. In fact, when the value 1 is used as the seed, you see the same “random” values you saw in Exercise 1, when you didn’t even use srand()!
There has to be a better way.
The best way to write a random-number generator is not to ask the user to type a seed, but rather to fetch a seed from elsewhere. In More Truly Random Than Ever, the seed value is pulled from the system clock by using the time() function.
MORE TRULY RANDOM THAN EVER
The time() function returns information about the current time of day, a value that’s constantly changing. The NULL argument helps solve some problems, but time() returns an ever-changing value.
The (unsigned) part of the statement ensures that the value returned by the time() function is an unsigned integer. That’s a technique known as typecasting.
The bottom line is that the srand() function is passed a seed value, courtesy of the time() function, and the result is that the rand() function generates values that are more random than you’d get otherwise.
Exercise 4: Type the source code from More Truly Random Than Ever and build the project. Run it a few times to ensure that the numbers are as random as the computer can get them.