# C++ Programming Code Examples

## C++ > Sorting Searching Code Examples

### Program to Implement Quick Sort with Given Complexity Constraint

/* Program to Implement Quick Sort with Given Complexity Constraint - Quick sort is based on an algorithmic design pattern called divide-and-conquer. - The average time complexity is O(n*log(n)) but the worst case complexity is O(n^2). - To reduce the chances of the worst case we have implemented Quicksort using randomization. - Here we will be selecting the pivot randomly. - Randomly select pivot value from the given subpart of the array. - Partition that subpart so that the values left of the pivot are smaller and to the right are greater from the pivot. - Consider both as new sub-array and repeat step 1 until only one element left in subpart. - Display the result. - Exit. C++ program to implement Quick sort using randomization. */ #include<iostream> #include<cstdlib> using namespace std; // Swapping two values. void swap(int *a, int *b) { int temp; temp = *a; *a = *b; *b = temp; } // Partitioning the array on the basis of values at high as pivot value. int Partition(int a[], int low, int high) { int pivot, index, i; index = low; pivot = high; // Getting index of pivot. for(i=low; i < high; i++) { if(a[i] < a[pivot]) { swap(&a[i], &a[index]); index++; } } // Swapping value at high and at the index obtained. swap(&a[pivot], &a[index]); return index; } // Random selection of pivot. int RandomPivotPartition(int a[], int low, int high) { int pvt, n, temp; n = rand(); // Randomizing the pivot value in the given subpart of array. pvt = low + n%(high-low+1); // Swapping pvt value from high, so pvt value will be taken as pivot while partitioning. swap(&a[high], &a[pvt]); return Partition(a, low, high); } // Implementing QuickSort algorithm. int QuickSort(int a[], int low, int high) { int pindex; if(low < high) { // Partitioning array using randomized pivot. pindex = RandomPivotPartition(a, low, high); // Recursively implementing QuickSort. QuickSort(a, low, pindex-1); QuickSort(a, pindex+1, high); } return 0; } int main() { int n, i; cout<<"\nEnter the number of data element to be sorted: "; cin>>n; int arr[n]; for(i = 0; i < n; i++) { cout<<"Enter element "<<i+1<<": "; cin>>arr[i]; } QuickSort(arr, 0, n-1); // Printing the sorted data. cout<<"\nSorted Data "; for (i = 0; i < n; i++) cout<<"->"<<arr[i]; return 0; }

Partition range in two. Rearranges the elements from the range [first,last), in such a way that all the elements for which pred returns true precede all those for which it returns false. The iterator returned points to the first element of the second group. The relative ordering within each group is not necessarily the same as before the call. See stable_partition for a function with a similar behavior but with stable ordering within each group. The function shall not modify its argument. This can either be a function pointer or a function object. Function returns an iterator that points to the first element of the second group of elements (those for which pred returns false), or last if this group is empty.

#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.

A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.

The cin object is used to accept input from the standard input device i.e. keyboard. It is defined in the iostream header file. C++ cin statement is the instance of the class istream and is used to read input from the standard input device which is usually a keyboard. The extraction operator(>>) is used along with the object cin for reading inputs. The extraction operator extracts the data from the object cin which is entered using the keyboard. The "c" in cin refers to "character" and "in" means "input". Hence cin means "character input". The cin object is used along with the extraction operator >> in order to receive a stream of characters.

In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement, The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.

Compute natural logarithm. Returns the natural logarithm of x. The natural logarithm is the base-e logarithm: the inverse of the natural exponential function (exp). For common (base-10) logarithms, see log10. The C/C++ library function double log(double x) returns the natural logarithm (base-e logarithm) of x. Function returns natural logarithm of x. If x is negative, it causes a domain error. If x is zero, it may cause a pole error (depending on the library implementation).

An array is defined as the collection of similar type of data items stored at contiguous memory locations. Arrays are the derived data type in C++ programming language which can store the primitive type of data such as int, char, double, float, etc. It also has the capability to store the collection of derived data types, such as pointers, structure, etc. The array is the simplest data structure where each data element can be randomly accessed by using its index number. C++ array is beneficial if you have to store similar elements. For example, if we want to store the marks of a student in 6 subjects, then we don't need to define different variables for the marks in the different subject. Instead of that, we can define an array which can store the marks in each subject at the contiguous memory locations.

The cout is a predefined object of ostream class. It is connected with the standard output device, which is usually a display screen. The cout is used in conjunction with stream insertion operator (<<) to display the output on a console. On most program environments, the standard output by default is the screen, and the C++ stream object defined to access it is cout. The "c" in cout refers to "character" and "out" means "output". Hence cout means "character output". The cout object is used along with the insertion operator << in order to display a stream of characters.

Generate random number. Returns a pseudo-random integral number in the range between 0 and RAND_MAX. This number is generated by an algorithm that returns a sequence of apparently non-related numbers each time it is called. This algorithm uses a seed to generate the series, which should be initialized to some distinctive value using function srand. RAND_MAX is a constant defined in <cstdlib>. The rand() function in C++ is used to generate random numbers; it will generate the same number every time we run the program. In order to seed the rand() function, srand(unsigned int seed) is used. The srand() function sets the initial point for generating the pseudo-random numbers. The rand() function generates numbers randomly.

A relational operator is used to check the relationship between two operands. C++ Relational Operators are used to relate or compare given operands. Relational operations are like checking if two operands are equal or not equal, greater or lesser, etc. Relational Operators are also called Comparison Operators.

Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code.

In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.

The 'Heapsort' is a comparison-based sorting algorithm. 'Heapsort' can be thought of as an improved 'Selection Sort': like that algorithm, it divides its input into a sorted & an unsorted

To find the length of the string in 'C++', ask to enter the string and then Find the Length the that string using function "strlen()" of string.h library and display the length value of a string

Bipartite Graph is a graph in which the set of 'vertices' can be divided into 2 sets such that all vertex should be present in either set 1 or set 2 but not both, and there should no edge

This algorithm takes the input of the 'specific' sequence. It generates random Subsequence from the given character string. A function to generate 'random' sequence of a given length