quicksort

void quicksort(int *a,int left,int right){
    if(left >= right){
        return ;
    }
    int i = left;
    int j = right;
    int key = a[left];
     
    while(i < j)                          
    {
        while(i < j && key <= a[j]){
            j--;
        }
        a[i] = a[j];
        while(i < j && key >= a[i]){
            i++;
        }
         
        a[j] = a[i];
    }
     
    a[i] = key;
    quicksort(a, left, i - 1);
    quicksort(a, i + 1, right);
}