Java Binary Search Help

[stereosteve99]

I can get it to compile, but it never gets to the part where it finds it or doesn't.. Goes through the while loop 4 times, no matter what the entry is.


public class BinarySearch

{

public static void main(String[] args) throws Exception

{

char[] orderedList = {'A','B','E','G','L','P','V','W','Y','Z'};

System.out.println("Enter a capital letter to search for: ");

int x = System.in.read();






int count = 0;
int low = 0;

int high = orderedList.length - 1;

while (low <= high) {

count++;
int mid = (low + high) / 2;



if (x < mid)

high = mid - 1;

else if (x > mid)

low = mid + 1;

else

System.out.println("It has been found!");

}

if (high > low)

System.out.println("Number wasn't found");

System.out.println(count);
}

}

 

[Cowboy Shane]

I will look again to make sure your algorithm is correct, but the biggest problem you have now is that you are mixing chars and ints.

You have a char array of capital letters, and then you read input with this line:
int x = System.in.read();
which java casts as an integer. The integer equivalent of a char is the character's ascii code (ie the ascii representation for 'A' is 65 which is well out of your search range).

You are also making a incorrect comparisons:
if (x < mid)
should be
if (x < orderedlist[mid])
Otherwise you are comparing the char you are searching for to the index of a char in the array.

Let me know if that was confusing, and I'll be glad to assist you further.

 

[stereosteve99]

Here's the update, now I have no idea why it doesn't work. If I enter L(the middle number) it works, otherwise it doesn't


public class BinarySearch


{


public static void main(String[] args) throws Exception


{


char[] orderedList = {'A','B','E','G','L','P','V','W','Y','Z'};


System.out.println("Enter a capital letter to search for: ");


int x = System.in.read();









int count = 0;

int low = 0;


int high = orderedList.length - 1;


while (low < high) {


count++;

int mid = (low + high) / 2;





if (x < orderedList[mid])


high = mid - 1;


else if (x > orderedList[mid])


low = mid + 1;


else


System.out.println("It has been found!");


high = low;
}


if (high > low)


System.out.println("Number wasn't found");


System.out.println(count);

}


}

 

[Cowboy Shane]

your variable x is still an int and it needs to be a char.

 

[stereosteve99]

Thanks for all your help on that one. I actually wanted to keep the x an integer because I was using the unicode, like you said earlier. The only thing I had to fix, which ****es me off so much, because it was so easy was putting curly brackets around all my if statements and I changed a couple small things. Now it works. But I always thought that if you only have one line after an if you didn't need the brackets.. God I hate programming..

Thanks again, that one had me stumpted (Which isn't saying much for me.)