public static void Main(string[] args)
{
// Input strings from file into string array (.txt file of numbers 1 to 10,000, unordered)
string[] readFile = File.ReadAllLines("/Users/redahanb/projects/courseraalgorithms_programming2/quicksort.txt");
// for testing purposes
//string[] readFile = File.ReadAllLines ("/Users/redahanb/projects/courseraalgorithms_programming2/1000.txt");
// copy and parse strings into new integer array
int[] convertedFile = new int[readFile.Length];
for (int i = 0; i < convertedFile.Length; i++)
{
convertedFile[i] = int.Parse(readFile[i]); // this is the file we work with
}
// Testing findMedian function
//Console.WriteLine (findMedian(new int[]{8,2,4,5,7,1}));
// Perform QuickSort operation
int[] sortedarray = QuickSort(convertedFile);
// testing
Console.WriteLine("");
for (int x = 0; x < 20; x++)
{
Console.WriteLine(sortedarray[x]);
}
// report back number of comparisons performed during QuickSort
Console.WriteLine("Comparisons performed: " + ComparisonCounter.reportCount().ToString());
} // main function/method
} // main function/method
public static int[] QuickSort(int[] input)
{
// Randomly select a pivot, P
int n = input.Length;
if (n < 2)
{
return(input);
}
else
{
// Set pivot index // 3 options here for each of three different parts of the assignment
//int pivot = 0; // question 1: pivot is first element
//int pivot = n-1; // question 2: pivot is last element
int pivot = findMedian(input); // question 3: pivot is median of 1st, last, and middle element
/////////////////////////////
///Partitioning the array///
////////////////////////////
int divide = 1; // integer to keep track of index between the 2 partitions
// put pivot at index 0 temporarily
swapEntry(ref input, 0, pivot);
// Sort the array to have entries less than the pivot to the left, and greater than the pivot to the right
for (int j = 1; j < n; j++)
{
if (input[j] < input[0])
{
// swap operation
swapEntry(ref input, divide, j);
divide++;
}
}
ComparisonCounter.incrementCount(n - 1);
// put the pivot element at the partition, dividing the array IN TWAIN
swapEntry(ref input, 0, divide - 1); // divide is the left-most element in the upper partition (> pivot value)
////////////////////////
///Recursive sorting ///
////////////////////////
// Split the array above and below the pivot
int[] arrayA = new int[divide - 1];
int[] arrayB = new int[n - divide];
Array.Copy(input, 0, arrayA, 0, divide - 1);
Array.Copy(input, divide, arrayB, 0, n - divide);
// Recursively call QuickSort() on the arrays on either side of the pivot
arrayA = QuickSort(arrayA);
// if(arrayA.Length > 1){
// ComparisonCounter.incrementCount (arrayA.Length - 1);
// }
arrayB = QuickSort(arrayB);
// if(arrayB.Length > 1){
// ComparisonCounter.incrementCount (arrayB.Length - 1);
// }
// create a return array to return the sorted arrays from the recursive calls, adding in the pivot inbetween
int[] returnArray = new int[n];
arrayA.CopyTo(returnArray, 0);
returnArray [divide - 1] = input [divide - 1];
arrayB.CopyTo(returnArray, divide);
return(returnArray);
}
} // QuickSort function
