Number of occurrence Java

PROGRAM TO COUNT THE NUMBER OF OCCURRENCES (OR FREQUENCY) IN A SORTED ARRAY



class MAIN
{
    /* if x is present in arr[] then returns 
       the count of occurrences of x, 
       otherwise returns -1. */
    static int count(int arr[], int x, int n)
    {
      // index of first occurrence of x in arr[0..n-1]    
      int i; 
        
      // index of last occurrence of x in arr[0..n-1]
      int j; 
           
      /* get the index of first occurrence of x */
      i = first(arr, 0, n-1, x, n);
       
      /* If x doesn't exist in arr[] then return -1 */
      if(i == -1)
        return i;
          
      /* Else get the index of last occurrence of x. 
         Note that we are only looking in the 
         subarray after first occurrence */  
      j = last(arr, i, n-1, x, n);     
          
      /* return count */
      return j-i+1;
    }
       
    /* if x is present in arr[] then returns the 
       index of FIRST occurrence of x in arr[0..n-1], 
       otherwise returns -1 */
    static int first(int arr[], int low, int high, int x, int n)
    {
      if(high >= low)
      {
        /*low + (high - low)/2;*/  
        int mid = (low + high)/2;  
        if( ( mid == 0 || x > arr[mid-1]) && arr[mid] == x)
          return mid;
        else if(x > arr[mid])
          return first(arr, (mid + 1), high, x, n);
        else
          return first(arr, low, (mid -1), x, n);
      }
      return -1;
    }
       
    /* if x is present in arr[] then returns the 
       index of LAST occurrence of x in arr[0..n-1], 
       otherwise returns -1 */
    static int last(int arr[], int low, int high, int x, int n)
    {
      if(high >= low)
      {
        /*low + (high - low)/2;*/      
        int mid = (low + high)/2; 
        if( ( mid == n-1 || x < arr[mid+1]) && arr[mid] == x )
          return mid;
        else if(x < arr[mid])
          return last(arr, low, (mid -1), x, n);
        else
          return last(arr, (mid + 1), high, x, n);      
      }
      return -1;
    }
       
    public static void main(String args[])
    {
        int arr[] = {1, 2, 2, 3, 3, 3, 3};
          
        // Element to be counted in arr[]
        int x =  3; 
        int n = arr.length;
        int c = count(arr, x, n);
        System.out.println(x+" occurs "+c+" times");
    }
}


OUTPUT
3 occurs 4 times

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