class PartitionIt
{
public static void partitionIt(int[] a, int l, int r, int pivot)
{
int i,j;
i = j = l+1;
while(j<= r)
{
if(a[j] <= a[pivot])
{
swap(a,j,i);
i++;
}
j++;
}
swap(a,pivot,--i);
}
public static void swap(int[] a, int j, int i)
{
int temp = a[j];
a[j] = a[i];
a[i] = temp;
}
public static void displayArray(int[] a)
{
for(int i:a)
System.out.print(i+" ");
System.out.println();
}
public static void QuickSort(int[] a, int l, int r)
{
if(r <= l)
return;
int pivot = getPivot(a,l,r);
partitionIt(a,l,r,pivot);
QuickSort(a,l,pivot);
QuickSort(a,pivot+1,r);
}
public static int getPivot(int[] a,int l,int r)
{
return l;
}
public static void main(String[] args)
{
int[] a = {3,2,8,5,1,4,7,6};
int[] b = {1,2,3,4,5,6,7,8,9,0};
int[] c = {5,4,2,4,7,6,5,3,2,1,10};
displayArray(a);
System.out.println("After Parititon with pivot 3");
QuickSort(a,0,a.length-1);
displayArray(a);
System.out.println();
displayArray(b);
System.out.println("After Parititon with pivot 1");
QuickSort(b,0,b.length-1);
displayArray(b);
System.out.println();
displayArray(c);
System.out.println("After Parititon with pivot 5");
QuickSort(c,0,c.length-1);
displayArray(c);
System.out.println();
}
}
3 2 8 5 1 4 7 6
After Parititon with pivot 3
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 9 0
After Parititon with pivot 1
0 1 2 3 4 5 6 7 8 9
5 4 2 4 7 6 5 3 2 1 10
After Parititon with pivot 5
1 2 2 4 3 4 5 5 6 7 10
It is not sorting properly in last case.
Can anyone help here. I m stuck from so long.
Thanks in advance!
At This snippet:
if(a[j] <= a[pivot])
{
swap(a,j,i);
i++;
}
The '<=' should be '<'.
while the sequence was sorted to 1 2 2 4 3 4 5 5 7 6 10,the pivot is '4'(the left one),while compare 4 <= 4,i++, this cause the swap(a,pivot,--i) change the location of '4'(the right one ) to '4'(the left one),rather than change the '3' to '4'.
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