Question

我正在尝试为整数数组编写递归排序算法。以下代码打印到控制台：3,5,2,1,1,2,6,7,8,10,20

输出应该排序，但不知何故“它不起作用”。

public static void main(String[] args)
{
    int[] unsortedList = {20, 3, 1, 2, 1, 2, 6, 8, 10, 5, 7};
    duplexSelectionSort(unsortedList, 0, unsortedList.length-1);

    for (int i = 0; i < unsortedList.length; i++)
    {
        System.out.println(unsortedList[i]);
    }
}


public static void duplexSelectionSort(
    int[] unsortedNumbers,
    int startIndex,
    int stopIndex)
{
    int minimumIndex = 0;
    int maximumIndex = 0;

    if (startIndex < stopIndex)
    {
        int index = 0;
        while (index <= stopIndex)
        {
            if (unsortedNumbers[index] < unsortedNumbers[minimumIndex])
            {
                minimumIndex = index;
            }
            if (unsortedNumbers[index] > unsortedNumbers[maximumIndex])
            {
                maximumIndex = index;
            }
            index++;
        }
        swapEdges(unsortedNumbers, startIndex, stopIndex, minimumIndex, maximumIndex);
        duplexSelectionSort(unsortedNumbers, startIndex + 1, stopIndex - 1);
    }
}


public static void swapEdges(
    int[] listOfIntegers,
    int startIndex,
    int stopIndex,
    int minimumIndex,
    int maximumIndex)
{
    if ((minimumIndex == stopIndex) && (maximumIndex == startIndex))
    {
        swap(listOfIntegers, startIndex, stopIndex);
    }
    else
    {
        if (maximumIndex == startIndex)
        {
            swap(listOfIntegers, maximumIndex, stopIndex);
            swap(listOfIntegers, minimumIndex, startIndex);
        }
        else
        {
            swap(listOfIntegers, minimumIndex, startIndex);
            swap(listOfIntegers, maximumIndex, stopIndex);
        }
    }
}

public static void swap(int[] listOfIntegers,
    int index1,
    int index2)
{
    int savedElementAtIndex1 = listOfIntegers[index1];
    listOfIntegers[index1] = listOfIntegers[index2];
    listOfIntegers[index2] = savedElementAtIndex1;
}

Answer 1

merge sort是一个众所周知的递归算法，你可以从中做出自己的递归排序算法：

public void mergeSort(int[] data) {
    if(data.length <= 1) return;               // Base case: just 1 elt

    int[] a = new int[data.length / 2];        // Split array into two
    int[] b = new int[data.length - a.length]; //   halves, a and b
    for(int i = 0; i < data.length; i++) {
        if(i < a.length) a[i] = data[i];
        else             b[i - a.length] = data[i];
    }

    mergeSort(a);                              // Recursively sort first
    mergeSort(b);                              //   and second half.

    int ai = 0;                                // Merge halves: ai, bi
    int bi = 0;                                //   track position in
    while(ai + bi < data.length) {             //   in each half.
        if(bi >= b.length || (ai < a.length && a[ai] < b[bi])) {
            data[ai + bi] = a[ai]; // (copy element of first array over)
            ai++;
        } else {
            data[ai + bi] = b[bi]; // (copy element of second array over)
            bi++;
        }
    }
}

Answer 2

您需要记住在递归方法中初始化变量时，您正在通过数组的stopIndex切片处理startIndex，而不是整个数组，并且您不应该触摸该切片之外的任何内容。

再看一下duplexSelectionSort方法中index，minimumIndex和maximumIndex的初始化。

Answer 3

这是我试过的一种递归排序。希望这可以帮助。与代码类似，但感觉有点复杂。

public static void main(String[] args)
{
int [] array = {5,9,2,3,10,20,1,7};
int len = array.length-1;
sort(array, 0, len);
for(int i=0;i<=len;i++)
{
  System.out.println(array[i]);
}
}

public static void sort(int[] array, int start, int end)
{
if (start < end)
{
  sort(array, start+1, end);
  if(array[start]<=array[end])
  {
    sort(array, start, end-1);
  }
  else if(array[start]>array[end])
  {
    int temp = array[start];
    array[start] = array[end];
    array[end] = temp;
    sort(array, start, end-1);
  }
}
else if(start == end)
  return;
}

Answer 4

您也可以使用选择排序方法。

应用递归样式是一种很好的算法。

public static int FindMinIndex(int[] data, int x, int y){

    int mini;

    if(x==y){
        mini=x;
    }

    else{
        int tempmini=FindMinIndex(data, x+1, y);
        if (data[tempmini]<data[x]){
            mini=tempmini;
        }
        else{
            mini=x;
        }
    }
    return mini;
}

//Do selection sort between data[x]~data[y]
public static void SelectionSort(int[] data, int x, int y){

    if (x==y){
        return;
    }

    else{
        int index=FindMinIndex(data, x, y);

        int temp=data[index];
        data[index]=data[x];
        data[x]=temp;

        SelectionSort(data,x+1,y);
    }

}

Answer 5

要从最小的数组中对数组进行排序，请执行以下操作：

Arrays.sort(array);

编写整数数组的递归排序算法

5 个答案: