How to write Binary Search algorithm in Java
Recursive Binary Search Implementation
The following code implements the binary search algorithm.
Its uses the Comparable interface to compare
elements in the passed in array.
Another feature is that it uses the recursive in the implementation.
public class Main {
public static final int NOT_FOUND = -1;
public static int binarySearch(Comparable[] a, Comparable x) {
return binarySearch(a, x, 0, a.length - 1);
}// ww w .j ava 2s.c o m
private static int binarySearch(Comparable[] a, Comparable x, int low, int high) {
if (low > high)
return NOT_FOUND;
int mid = (low + high) / 2;
if (a[mid].compareTo(x) < 0)
return binarySearch(a, x, mid + 1, high);
else if (a[mid].compareTo(x) > 0)
return binarySearch(a, x, low, mid - 1);
else
return mid;
}
public static void main(String[] args) {
int SIZE = 8;
Comparable[] a = new Integer[SIZE];
for (int i = 0; i < SIZE; i++)
a[i] = new Integer(i * 2);
for (int i = 0; i < SIZE * 2; i++)
System.out.println("Found " + i + " at " + binarySearch(a, new Integer(i)));
}
}
The code above generates the following result.
Binary search without recursive
The following code uses the binary search algorithm to search a hard code array against hard coded value.
public class Main{
public static void main(String[] args) {
double[] x = { -39, -3, 6, 10, 4, 9, 10 };
//from w ww. j a v a 2s. com
double value = 8;
int lower = 0, upper = x.length - 1;
while (lower <= upper) {
int middle = (lower + upper) / 2;
if (value > x[middle])
lower = middle + 1;
else if (value < x[middle])
upper = middle - 1;
else
break;
}
if (lower > upper)
System.out.println("Not found");
else
System.out.println("Found");
}
}
The code above generates the following result.
Binary Search Insert
public class Main{
public static void main(String[] args) {
int maxSize = 100;
BinarySearchArray arr = new BinarySearchArray(maxSize);
arr.insert(2);//from w ww. j ava 2 s .co m
arr.insert(0);
arr.insert(5);
arr.insert(6);
arr.insert(4);
arr.insert(9);
arr.insert(4);
arr.insert(7);
arr.insert(5);
arr.insert(9);
arr.insert(8);
arr.insert(2);
arr.insert(4);
arr.insert(6);
arr.insert(8);
arr.insert(9);
arr.display(); // display array
int searchKey = 27; // search for item
if (arr.find(searchKey) != arr.size())
System.out.println("Found " + searchKey);
else
System.out.println("Can't find " + searchKey);
}
}
class BinarySearchArray {
private long[] a;
private int nElems;
public BinarySearchArray(int max) {
a = new long[max]; // create array
nElems = 0;
}
public int size() {
return nElems;
}
public int find(long searchKey) {
return recFind(searchKey, 0, nElems - 1);
}
private int recFind(long searchKey, int lowerBound, int upperBound) {
int curIn;
curIn = (lowerBound + upperBound) / 2;
if (a[curIn] == searchKey)
return curIn; // found it
else if (lowerBound > upperBound)
return nElems; // can't find it
else // divide range
{
if (a[curIn] < searchKey) // in upper half
return recFind(searchKey, curIn + 1, upperBound);
else
// in lower half
return recFind(searchKey, lowerBound, curIn - 1);
}
}
public void insert(long value) {
int j;
for (j = 0; j < nElems; j++)
// find where it goes
if (a[j] > value) // (linear search)
break;
for (int k = nElems; k > j; k--)
// move bigger ones up
a[k] = a[k - 1];
a[j] = value; // insert it
nElems++; // increment size
}
public void display() {
for (int j = 0; j < nElems; j++)
System.out.print(a[j] + " ");
System.out.println("");
}
}
The code above generates the following result.
0 2 2 4 4 4 5 5 6 6 7 8 8 9 9 9
Can't find 27