Question

Need a simple C++ code that read a text file of integers, puts the integers in a array and using quick sort, sorts the numbers.

Answer 1

#include <iostream>

#include <fstream>

using namespace std;

// A utility function to swap two elements

void swap(int* a, int* b)

{

int t = *a;

*a = *b;

*b = t;

}

/* This function takes last element as pivot, places

the pivot element at its correct position in sorted

array, and places all smaller (smaller than pivot)

to left of pivot and all greater elements to right

of pivot */

int partition (int arr[], int low, int high)

{

int pivot = arr[high]; // pivot

int i = (low - 1); // Index of smaller element

for (int j = low; j <= high- 1; j++)

{

// If current element is smaller than or

// equal to pivot

if (arr[j] <= pivot)

{

i++; // increment index of smaller element

swap(&arr[i], &arr[j]);

}

}

swap(&arr[i + 1], &arr[high]);

return (i + 1);

}

/* The main function that implements QuickSort

arr[] --> Array to be sorted,

low --> Starting index,

high --> Ending index */

void quickSort(int arr[], int low, int high)

{

if (low < high)

{

/* pi is partitioning index, arr[p] is now

at right place */

int pi = partition(arr, low, high);

// Separately sort elements before

// partition and after partition

quickSort(arr, low, pi - 1);

quickSort(arr, pi + 1, high);

}

}

/* UTILITY FUNCTIONS */

/* Function to print an array */

void printArray(int A[], int size)

{

int i;

for (i=0; i < size; i++)

cout<<A[i]<<" ";

cout<<endl;

}

int main(int argc, char * argv[])

{

string inFile;

cout<<"Enter input file name: ";

cin>>inFile;

std::fstream myfile(inFile, std::ios_base::in);

int a;

int arr[1000];

int i = 0;

while (myfile >> a)

{

arr[i] = a;

i++;

}

myfile.close();

printArray(arr, i);

quickSort(arr, 0, i-1);

printArray(arr, i);

return 0;

}

######### input.txt #########
4
3
12
6
7
1
0
56
21

fourthweek fourthweek fourthweek g++ quickSort.cpp fourthweek./a.out Enter input file name: input.txt 4 3 12 6710 56 21 013 467 12 21 56 fourthweek