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Zython
Registered User regular

Ok, I need to do a quicksort rotuine for my class. I have the following:

The goal being to find the k-th smallest element in an array.

I also have to do one that's better suited for this purpose, what I have:'

The problem is that I sometimes get an OutofBoundsIndex Exception at the lines bolded above. Can anyone tell me what I'm doing wrong? If you have any questions, feel free to ask.

Edit: Made problematic lines more visible.

Edit: Found the problem, the for loop wasn't breaking properly, changed to a while loop.

```
public static int quicksort(int A[], int k){
quicksort(A, 0, A.length - 1);
return A[k-1];
}
private static void swap(int A[], int a, int b){
int key = A[a];
A[a] = A[b];
A[b] = key;
}
private static int median(int A[], int left, int right){
int center = (left + right)/2;
int key = 0;
if(A[center] < A[left]){
swap(A, left, center);
}
if(A[right] < A[left]){
swap(A, left, right);
}
if(A[right] < A[center]){
swap(A, center, right);
}
swap(A, center, right - 1);
return A[right - 1];
}
private static void quicksort(int A[], int left, int right){
if(left + 1 <= right){
int pivot = median(A, left, right);
int i = left, j = right - 1;
for( ; ;){
while(A[++i] <= pivot){
}
%% [b]while(A[--j] > pivot){[/b]
}
if(i < j){
swap(A, i, j);
}
else{
break;
}
}
swap(A, i, right - 1);
%%%% [b]quicksort(A, left, i - 1);[/b]
quicksort(A, i + 1, right);
}
}
```

The goal being to find the k-th smallest element in an array.

I also have to do one that's better suited for this purpose, what I have:'

```
public static int quickersort(int A[], int k){
quickersort(A, 0, A.length - 1, k);
return A[k - 1];
}
private static void quickersort(int A[], int left, int right, int k){
if(left + 1 <= right){
int pivot = median(A, left, right);
int i = left, j = right - 1;
for( ; ;){
while(A[++i] < pivot){
}
%% [b]while(A[--j] > pivot){[/b]
}
if(i < j){
swap(A, i, j);
}
else{
break;
}
}
swap(A, i, right - 1);
if(k <= i){
%% [b]quickersort(A, left, i - 1, k);[/b]
}
else if(k > i + 1){
quickersort(A, i + 1, right, k);
}
}
}
```

The problem is that I sometimes get an OutofBoundsIndex Exception at the lines bolded above. Can anyone tell me what I'm doing wrong? If you have any questions, feel free to ask.

Edit: Made problematic lines more visible.

Edit: Found the problem, the for loop wasn't breaking properly, changed to a while loop.

0

## Posts

If you're not using an IDE with a debugger, just stick some System.out.println() in there with the values.

Jimmy Kingon