[algogeeks] Re: Can anyone point out the mistakes in my program?

Sun, 25 Jun 2006 18:13:36 -0700

I did not get to read the program completely or run it or test it, but my surmise is you are not incrementing left pointer and decrementing right pointer after swapping as I have indicated below.

On 6/25/06, Thomas.Chang <[EMAIL PROTECTED]> wrote:

Following is a qsort() program, I checked it carefully severally times
and tested with a lot of cases without finding any error. But when I
submit the program using it to online judge, it always "wrong answer",
if I substitute it with the standard qsort() of c library, it will
pass.
I post it here wishing someone can point out my mistakes. It's really
frustrating having problem with such basic, simple algorithms.

-----------------------------------------------------------------------------------
int sticks[100];
void sort(int left,int right){
        int pivot, i, j;
        int temp;
        if(left<right){
                i=left; j=right+1;
                pivot = sticks[left];
                do{
                        do i++;
                        while (i<=right && sticks[i] < pivot );
                        do j--;
                        while (j>=left && sticks[j] > pivot);
                        if(i<j && i<=right && j>=left) {
                                temp = sticks[i];
                                sticks[i] = sticks[j];
                                sticks[j] = temp;
                        } // <potentialBug> need an increment/decrement on swap </potentialBug>
                }while(i<j);
                if(j>left){
                        temp = sticks[left];
                        sticks[left] = sticks[j];
                        sticks[j] = temp;
                }
                if(left<j) sort(left,j-1);
                if(j<right && left<=j) sort(j+1, right);
        }
}



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