/*
 * @!RadixSortAlgorithm.java
 * By: Alvin Raj
 * Date: 12 August 2002
 * Algorithm adapted from: C++ Data Structures, Nell Dale
 * Additional Comments added by Jason Harrison <harrison@cs.ubc.ca>
 *
 *  Algorithm comments from
 *  http://ciips.ee.uwa.edu.au/~morris/Year2/PLDS210/radixsort.html
 *
 */
public class RadixSortAlgorithm extends SortAlgorithm {

// for each of the 10 digits
   private LinkedQueue[] Q =
     { new LinkedQueue(),  //0
       new LinkedQueue(),  //1
       new LinkedQueue(),  //2
       new LinkedQueue(),  //3
       new LinkedQueue(),  //4
       new LinkedQueue(),  //5
       new LinkedQueue(),  //6
       new LinkedQueue(),  //7
       new LinkedQueue(),  //8
       new LinkedQueue()}; //9

	// Assumes all positive integers
        // numbDigits is the number of digits in the largest number
	void sort(int a[] , int numDigits) throws Exception {
		int arrayPos;
		// i is the radix
		for (int i = 1; i <= numDigits; i++) {
			if (stopRequested) {
				return;
			}
			arrayPos = 0;
			// Put values into queues according to radix
                        // least significant digit first, then second,...
                        // first pass sorts on least significant digit
			for (int j = 0; j < a.length; j++) {
				Q[getRadix(a[j],i)].enqueue(a[j]);
                                pause(-1,j); // JH
			}
			// Collect the queues and put them back into the array
                        // queues contain partially sorted lists after first
                        // pass -- moving to next significant digit will
                        // maintain this ordering.
			for (int j = 0; j < Q.length; j++) {
				while(!Q[j].isEmpty()) {
					a[arrayPos] = Q[j].dequeue();
					arrayPos++;
				}
				pause(-1,arrayPos);
			}
		}
	}

	void sort(int a[]) throws Exception {
		// Find the largest entry in a[]
		int max = 0;
                int maxIndex = 0;  // JH
		for (int i = 0; i < a.length; i++) {
			if (max < a[i]) {
                            max = a[i];
                            maxIndex = i; // JH
                            pause(maxIndex, i); // JH
			}
		}

		int numDigits = 1;
		int temp = 10;
                // compute the max number of digits
                // JH: this could be more easily be computed by using
                //     numDigits = (int) log(base10, max)
		while (true) {
			if (max >= temp) {
				numDigits++;
				temp*=10;
			}
			else
				break;
		}

		//call the sort
		sort(a,numDigits);
	}

	//returns the radix of the given number
	//EG:
	//2nd radix of 79981 is 8
	//1st radix of 79981 is 1
	public static int getRadix(int number, int radix) {
		return (int)(number / Math.pow(10,radix-1)) % 10;
	}


}