title: Studying the Quicksort algorithm
body: <p>I study the Quicksort algorithm and created a sample program like this :  </p>
  
  <pre><code>// Java program for implementation of QuickSort 
  class QuickSort 
  { 
  /* This function takes last element as pivot, 
  places the pivot element at its correct 
  position in sorted array, and places all 
  smaller (smaller than pivot) to left of 
  pivot and all greater elements to right 
  of pivot */
      int partition(int arr[], int low, int high) 
      { 
          int pivot = arr[high]; 
          int i = (low-1); // index of smaller element 
  
          for (int j=low; j&lt;high; j++) 
          { 
              // If current element is smaller than or 
              // equal to pivot 
              if (arr[j] &lt;= pivot) 
              { 
                  i++; 
  
                  // swap arr[i] and arr[j] 
                  int temp = arr[i]; 
                  arr[i] = arr[j]; 
                  arr[j] = temp; 
              } 
          } 
  
          // swap arr[i+1] and arr[high] (or pivot) 
          int temp = arr[i+1]; 
          arr[i+1] = arr[high]; 
          arr[high] = temp; 
  
          return i+1; 
      } 
  
      /* The main function that implements QuickSort() 
      arr[] --&gt; Array to be sorted, 
      low --&gt; Starting index, 
      high --&gt; Ending index */
  
      void sort(int arr[], int low, int high) 
      { 
          if (low &lt; high) 
          { 
              /* pi is partitioning index, arr[pi] is 
              now at right place */
              int pi = partition(arr, low, high); 
  
              // Recursively sort elements before 
              // partition and after partition 
              sort(arr, low, pi-1); 
              sort(arr, pi+1, high); 
          } 
      } 
  
      /* A utility function to print array of size n */
      static void printArray(int arr[]) 
      { 
          int n = arr.length; 
          for (int i=0; i&lt;n; ++i) 
              System.out.print(arr[i]+" "); 
          System.out.println(); 
      } 
  
      // Driver program 
      public static void main(String args[]) 
      { 
          int arr[] = {10, 7, 8, 9, 1, 5}; 
          int n = arr.length; 
  
          QuickSort ob = new QuickSort(); 
          ob.sort(arr, 0, n-1); 
  
          System.out.println("sorted array"); 
          printArray(arr); 
      } 
  } 
  /*This code is contributed by Rajat Mishra */
  </code></pre>
  
  <p>Precisely in this part : </p>
  
  <pre><code>int partition(int arr[], int low, int high) 
  { 
      int pivot = arr[high];  
      int i = (low-1); // index of smaller element 
      for (int j=low; j&lt;high; j++) 
  </code></pre>
  
  <p>would you have an idea why the code says: <code>int i = (low-1)</code> ? The range of <code>i</code> will not become -1 with this instruction? I mean it was initialized previously to 0? Then do think is it possible such instruction? Or what as you it has to understand?</p>
  
  <p>Best regard, 
  Thanks, 
  Intelego. </p>