Binary Search in Java

Binary Search in Java

Binary Search in Java


In binary search the array must be in sorted order either ascending or descending order. Binary search relies on divide and conquer strategy in a sorted list. In Binary Search we split the array into two half. And then check the search value, if the value is less than the mid value then we will only look First half otherwise Second half. In this way we will search until the value found.  

Logic :
In this example I have declare array num[]. After then I insert the value. Then with the help of Bubble sort algorithm we do the sorting. After then a search value has taken. Here first of all the desired elements compared with the middle most elements of the array.
If the search element is smaller to the middle most elements then process is repeated with the first half of the array.
If the search element is greater to the middle most elements then process is repeated with the second half of the array.
If the search element is equal to the middle most elements search is completed and position is return in ‘pos ‘ variable.


import java.io.*;
/**
 * BinarySearchInJava
 *  Array must be in sorted order for Binary search
 */
public class BinarySearchInJava
{
    public static void main(String args[]) throws IOException
    {
        int num[] = new int[10];
        int i,s,f=0,t,j;
        int low, high, mid, pos;
        InputStreamReader in=new InputStreamReader(System.in);
        BufferedReader br=new BufferedReader(in);
        System.out.println("Enter elements in array:");
        for(i=0;i<10;i++)
        {
            num[i] = Integer.parseInt(br.readLine());
        }
        System.out.println("Enter element to Search:");
        s = Integer.parseInt(br.readLine());
        // Sorting of array
        for(i=0;i<9;i++)
        {
            for(j=0;j<9-i;j++)
            {
                if(num[j] > num[j+1])
                {
                    t = num[j];
                    num[j] = num[j+1];
                    num[j+1] = t;
                }
            }
        }
        System.out.println("Sorted array:");
        for(i=0;i<10;i++)
        {
            System.out.print(num[i] + " ");
        }
        // Binary Search
        high=10;
        low=0;
        pos=0;
        while(low <= high)
        {
            mid = (low + high) / 2;
            if(s < num[mid])
            {
                high = mid - 1;
            }
            else if(s>num[mid])
            {
                low = mid + 1;
            }
            else if(s == num[mid])
            {
                pos = mid + 1;
                break;
            }
        }
        System.out.println("\n Search result");
        System.out.println(s+" is located at " + pos);
    }
}

Output:
Enter elements in array:
10
7
8
4
5
6
9
1
2
3
Enter element to Search:
4
Sorted array:
1 2 3 4 5  6 7 8 9 10
 Search result
4 is located at 4
Variable Description for Java:
Sl. No.
Variable Name
Data Type
Purpose
1
main()
void
Main function
2
num[]
int
To store the values in an array
3
i , j
int
For running the loop
4
s
int
To store the input (element to be searched)
5
t
int
For temporarily storing a value
6
low
int
  value in the lowest position
7
mid
int
 value in the middle position
8
high
int
  value in the highest position
9
pos
int
 position of the value which was searched(only if exists)
10
in
InputStreamReader
To instantiate the InputStreamReader class which exists in java.iopackage
11
br
BufferedReader
To instantiate the BufferedReader class which exists in java.iopackage using the above variable as passing parameter

Analysis:


Here we are reducing the search area. Here number of comparisons keeps on decreasing. In worst case scenario log(N + 1), that is why it is an efficient search compared to Linear Search. 

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