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toogreat4u

Java exercise using Binary Search ?

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I am reading from introduction to java 7th edition and I have run into a programming exercise that has me baffled. I understand the code samples in the book but I am completely confused as to what they are trying to get me to do. The program exercise has this description: (Financial application: finding the sales amount) Rewrite Listing 4.9, FindSalesAmount.java using the binary search approach. Since the sales amount is between 1 and COMMISSION_SOUGHT / 0.08, you can use a binary search to improve it. Here is there Listing 4.9
public class FindSalesAmount {
  /** Main method */
  public static void main(String[] args) {
    // The commission sought
    final double COMMISSION_SOUGHT = 25000;
    final double INITIAL_SALES_AMOUNT = 0.01;
    double commission = 0;
    double salesAmount = INITIAL_SALES_AMOUNT;

    do {
      // Increase salesAmount by 1 cent
      salesAmount += 0.01;

      // Compute the commission from the current salesAmount;
      if (salesAmount >= 10000.01)
        commission =
          5000 * 0.08 + 5000 * 0.1 + (salesAmount - 10000) * 0.12;
      else if (salesAmount >= 5000.01)
        commission = 5000 * 0.08 + (salesAmount - 5000) * 0.10;
      else
        commission = salesAmount * 0.08;
    } while (commission < COMMISSION_SOUGHT);

    // Display the sales amount
    System.out.println(
      "The sales amount $" + (int)(salesAmount * 100) / 100.0 +
      "\nis needed to make a commission of $" + COMMISSION_SOUGHT);
  }
}

Here is there binarySearch:
public class BinarySearch {
  /** Use binary search to find the key in the list */
  public static int binarySearch(int[] list, int key) {
    int low = 0;
    int high = list.length - 1;

    while (high >= low) {
      int mid = (low + high) / 2;
      if (key < list[mid])
        high = mid - 1;
      else if (key == list[mid])
        return mid;
      else
        low = mid + 1;
    }

    return -low - 1; // Now high < low
  }
}

What are they trying to get me to do with binary search and FindSalesAmount? I understand both programs seperately however I have no clue as to how they can be combined int one program as in the problem description. Any help is greatly appreciated. Thanks!

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I don't think they're asking you to use the actual BinarySearch class; they just want you to use the algorithm.

Do you see that do..while loop in FindSalesAmount? It's an incremental search. It checks salesAmount = 0.02, then salesAmount = 0.03, then salesAmount = 0.04, and so on, until it finds the right commission. What they're saying is that you should try a different search strategy - a binary search - checking different values of salesAmount so that you find the result more quickly.

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