// Routines to sort arrays of integers.
// (c) 1997 duane a. bailey

import structure.*;

public class MergeSort
{
    //+mergeSort
    public static void mergeSort(int data[], int n)
    // pre: 0 <= n <= data.length
    // post: values in data[0..n-1] are in ascending order
    {
	mergeSortRecursive(data,new int[n],0,n-1);
    }
    //-mergeSort
	
    //+mergeSortRecursive
    private static void mergeSortRecursive(int data[], 
					   int temp[], 
					   int low, int high)
    // pre: 0 <= low <= high < data.length
    // post: values in data[low..high] are in ascending order
    {
	int n = high-low+1;
	int middle = low + n/2;
	int i;

	if (n < 2) return;
	// move lower half of data in to temporary storage
	for (i = low; i < middle; i++)
	{
	    temp[i] = data[i];
	}
	// sort lower half of array
	mergeSortRecursive(temp,data,low,middle-1);
	// sort upper half of array
	mergeSortRecursive(data,temp,middle,high);
	// merge halves together
	merge(data,temp,low,middle,high);
    }
    //-mergeSortRecursive
	
    //+mergeOperation
    private static void merge(int data[], int temp[],
			      int low, int middle, int high)
    // pre: data[middle..high] are ascending
    //      temp[low..middle-1] are ascending
    // post: data[low..high] contains all values in ascending order
    {
	int ri = low; // result index
	int ti = low; // temp index
	int di = middle; // destination index
	// while two lists are not empty merge smaller value
	while (ti < middle && di <= high)
	{
	    if (data[ti] < temp[di]) data[ri++] = data[di++];
	    else data[ri++] = temp[ti++];
	}
	// possibly some values left in temp array
	while (ti < middle)
	{
	    data[ri++] = temp[ti++];
	}
	// ...or possibly some values left (in correct place) in data array
    }
    //-mergeOperation
    //+swap
    public static void swap(int data[], int i, int j)
    // pre: 0 <= i,j < data.length
    // post: data[i] and data[j] are exchanged
    {
	int temp;
	temp = data[i];
	data[i] = data[j];
	data[j] = temp;
    }
    //-swap
	
    //+vectorSort

    public static void swap(Vector data, int i, int j)
    // pre: 0 <= i,j < data.size()
    // post: i-th j-th elements of data are exchanged
    {
	Object temp;
	temp = data.elementAt(i);
	data.setElementAt(data.elementAt(j),i);
	data.setElementAt(temp,j);
    }
    //-vectorSort
}