Hoare Partition Correctness in java

问题

I am working to implement a Hoare partition into a quicksort. I am trying to completely understand the hoare partition but the book doesnt explain everything. Mainly I am just wondering what the while TRUE part means? The excerpt from the book is below. If I were to put the while part in java what would I use and why?

Hoare-Partition(A,p,r)
    x= A[p]
    i = p-1
    j=r+1
    while true
        repeat
            j=j-1
        until A [j] <= x
        repeat
            i = i +1
        until A[i] >= x
        if i < l
           exchange A[i] with A[j]
        else return j

回答1:

try this code for the algo that you have above :

int HoarePartition (int a[],int p, int r) 
{
    int x=a[p],i=p-1,j=r+1;
    while (true) 
    {
        while (a[j] <= x) j--; 
        while (a[i] >= x) i++;
        if  (i < j) swap(a[i],a[j]);
        else return j;
    }
}

回答2:

Here's a working translation:

  public static void quicksort(int[] ar) {
    if (ar == null) return;
    quicksort(ar, 0, ar.length-1);
  }

  private static void quicksort(int[] ar, int lo, int hi) {
    if (lo < hi) {
      int splitPoint = partition(ar, lo, hi);
      quicksort(ar, lo, splitPoint);
      quicksort(ar, splitPoint+1, hi);
    }
  }

  private static int partition(int[] ar, int lo, int hi) {
    int pivot = ar[lo];
    int i = lo-1, j = hi+1;
    while(true) {
      do { i++; } while(ar[i] < pivot);
      do { j--; } while(ar[j] > pivot);
      if (i < j) swap(ar, i, j);
      else return j;
    }
  }

  private static void swap(int[] ar, int i, int j) {
    int tmp = ar[i];
    ar[i] = ar[j];
    ar[j] = tmp;
  }

来源：https://stackoverflow.com/questions/15127540/hoare-partition-correctness-in-java

标签

java

quicksort