selectionsort.java

java编程代码

public class SelectionSort
{
    /**
     Precondition: numberUsed <= a.length;
                  The first numberUsed indexed variables have values.
     Action: Sorts a so that a[0] <= a[1] <= ... <= a[numberUsed - 1].
    */
    public static void sort(double[] a, int numberUsed)
    {
        int index, indexOfNextSmallest;
        for (index = 0; index < numberUsed - 1; index++)
        {//Place the correct value in a[index]:
            indexOfNextSmallest = indexOfSmallest(index, a, numberUsed);
            interchange(index,indexOfNextSmallest, a);
            //a[0] <= a[1] <=...<= a[index] and these are the smallest
            //of the original array elements. The remaining positions
            //contain the rest of the original array elements.
        }
    }

    /**
     Returns the index of the smallest value among
     a[startIndex], a[startIndex+1], ... a[numberUsed - 1]
    */
    private static int indexOfSmallest(int startIndex,
                                              double[] a, int numberUsed)
    {
        double min = a[startIndex];
        int indexOfMin = startIndex;
        int index;
        for (index = startIndex + 1; index < numberUsed; index++)
            if (a[index] < min)
            {
                min = a[index];
                indexOfMin = index;
                //min is smallest of a[startIndex] through a[index]
            }
        return indexOfMin;
    }
    
    /** 
     Precondition: i and j are legal indices for the array a.
     Postcondition: Values of a[i] and a[j] have been interchanged.
    */
    private static void interchange(int i, int j, double[] a)
    {
        double temp;
        temp = a[i];
        a[i] = a[j];
        a[j] = temp; //original value of a[i]
    }
    
}