I'm new to binary searches and I tried a program that would find the position of a value inputted by a user. My code however only seems to return a low=-1 value which leads to the program saying "the value was not found". I think I did something wrong with my binary search code, but I am not experienced with these and may have missed something? Here's my code for the binary search:
static public int search (int[]numbers,int target, int count)
{
int high = numbers.length;
int low = -1;
int middle = (high+low)/2;
while(high-low>1)
{
count++;
middle = (high+low)/2;
if(numbers[middle]>target)
{
high = middle;
}
else if(numbers[middle]<target)
{
low = middle;
}
else if(numbers[middle] == target)
{
break;
}
System.out.println(numbers[middle]);
System.out.println(middle);
}
if(low == -1 || numbers[low]!=target)
{
low=-1;
return low;
}
else
{
return low;
}
}
And here is part of the code which asks users for an input:
public static void main(String[] args) throws IOException {
DataInputStream input = new DataInputStream(System.in);
int [] numbers = new int [50000];
int target;
int count=0;
try
{
BufferedReader br = new BufferedReader(new FileReader("randNums.txt"));
for(int i=0;i<50000;i++)
{
numbers[i]=Integer.parseInt(br.readLine());
}
br.close();
Arrays.sort(numbers);
System.out.print("Choose a number between 1-100000000 to search for: ");
target = Integer.parseInt(input.readLine());
int low = search(numbers, target, count);
if(low==-1)
{
System.out.println("The number was not on the list.");
}
else
{
System.out.println("The number is at position " + low);
System.out.println("It took " + count + " comparisons to find the number.");
}
}
Your search function has some issues. The implementation of the binary search in the search function should be like this:
static public int search (int[]numbers,int target, int count)
{
int high = numbers.length-1;
int low = 0;
int middle = (high+low)/2;
while(high>=low)
{
count++;
middle = (high+low)/2;
if(numbers[middle]==target)
{
return middle;
}
else if(numbers[middle]<target)
{
low = middle+1;
}
else if(numbers[middle]>target)
{
high=middle-1;
}
System.out.println(numbers[middle]);
System.out.println(middle);
}
return -1;
}