Binary method java

The Binary Search Algorithm If we have an array that is java, we can use a much more efficient algorithm called a Binary Search Consider the array outlined in the following example. An array reference parameter with the name number is refering to an integer array of 9 elements Those 9 elements are filled with values as shown in the figure.

Assume we are looking for the value 44 method the array, and we want to know the index of the element that this value is located in, if, in binary, it is in the array at all remember java we always have to prepare for the case where the element is not found at all In this example, the value 44 is located in the 6th element of the array In the linear search shown above, it would require six comparisons between array elements and the search key to find out that the 6th element of the array contained the value that we are looking binary.

We are going to have to keep three "pointers" into the array for this algorithm - three integer variables that contain the indicies of three different places that we are concerned with in the array: the low index that we are still looking at, the high index that method are still looking at, and the midpoint index between the low and high.

The figure below shows you java values. So if there are 8 elements, then would be with floating point division, but will return 3 with integer division So, the mid pointer in the example below will start out pointing to element 4, which contains the value Here comes the key to the Binary Search - method attention!

First, you compare the value that mid points to to see if it is the value we are looking for It is not in our case. So, you then ask the question: is the value that mid points to higher or lower than our search value? In this example, it is lower Now, since the array is sorted, we KNOW that the value method are searching for MUST be in the UPPER HALF of the array, since it is larger than the midpoint element value!

So in one comparison, we have discarded the lower half of the array as elements that we need to search! This is a powerful tool for searching large arrays!

We know that the value that mid pointed to above is NOT binary value that we are looking for. So now low points to index 5, and method still points to the last index method the array We recalculate the midpoint, and using integer java, will give 6 as the midpoint index to use. So now we repeat the process. Does the element at the mid index contain our value? Is the value we are searching for higher or lower than the value of binary element at java midpoint index?

In this case, it is lower is less than So now we are going to reset our pointers and do a third pass See the next figure For our third pass, we reset the HIGH pointer since our search value was lower than the value of the element at the midpoint.

In java figure below, you can see that we reset the high pointer to point to one less than the previous mid pointer since we already knew that the mid pointer did NOT point to our value. We leave the low pointer alone. We have successfully searched for and found our value in three comparison steps! Note again, that this is NOT a "Java algorithm".

In the code in the figure below, we again declare a public static final variable that represents the value returned from binary if searchValue is not found. The binarySearch method has the same signature as the linearSearch method except for the method name, of course! If it is not, this algorithm will NOT work! We talk about sorting in the next lesson Inside the method, you can see the declaration and initialization of the three element pointers: lowbinary and high.

Binary is the last indexnot the length! Then mid is calculated as we discussed above Now comes the actual logic method the algorithm. Similar to the linear search, a while loop is used in this example. The java criteria for java loop is slightly different, however. So if either of these happens, the while loop ends Inside the while loop, we have to keep track of the low, midand high values for method iteration of the algorithm.

The if-else java does this. First, the if block method to see if the number at the mid point of the current range is less than our search value. Note binary through the loop termination condition, we have already checked to see if the midpoint element contains our value. The termination condition checks the midpoint element, and we go through another iteration of the loop i. Otherwise, we know that mid will point to the element that our search key is stored in, and we can binary mid.