Arrays.binarySearch() in Java with examples | Set 2 (Search in subarray)

Arrays.binarySearch()| Set 1 Covers how to find an element in a sorted array in Java. This set will cover "How to Search a key in an array within a given range including only start index".

Syntax :  

public static int binarySearch(data_type[] arr, int fromIndex, int toIndex, data_type key)

Parameters :

arr – the array to be searched

fromIndex – the index of the first element (inclusive) to be searched

toIndex - the index of the last element (exclusive) to be searched

 key  – the value to be searched for 

• It is a static inbuilt method defined in Arrays (java.util.Arrays) class in java and returns the index of the specified key is found within the specified range.
• Here, data_type can be any of the primitive data_type: byte, char, double, int, float, short, long and Object as well.
• The above function Searches a range of the specified array of the given data type for the specified key using a binary search algorithm.
• The range within which the specified key to be searched must be sorted (as by the Arrays.sort() method) prior to making this call. Otherwise, the result would be undefined. If the specified array contains multiple values same as the specified key, there is no guarantee which one will be found.

Returns : 
Index of the specified key is found within the specified range in the specified array, Otherwise (-(insertion point) - 1). 

The insertion point is defined as a point at which the specified key would be inserted: the index of the first element in the range greater than the key, or toIndex if all elements in the range are less than the specified key. 
Note: This guarantees that the return value will be >= 0 if and only if the key is found.

Examples:  

   byteArr[] = {10,20,15,22,35}

   key = 22 to be searched between the range 2 to 4 in specified array.

   Output: 3

   charArr[] = {'g','p','q','c','i'}

   key = p to be searched between the range 1 to 4 in specified array.

   Output: 3

   intArr[] = {1,2,3,4,5,6}

   key = 3 to be searched between the range 1 to 4 in specified array.

   Output: 2

   doubleArr[] = {10.2,1.51,2.2,3.5}

   key = 1.5 to be searched between the range 1 to 4 in specified array.

   Output: -2 as it is the insertion point of 1.5

   floatArr[] = {10.2f,15.1f,2.2f,3.5f}

   key = 35.0 to be searched between the range 1 to 4 in specified array.

   Output: -5

  shortArr[] = {10,20,15,22,35}

  key = 5 to be searched between the range 0 to 4 in specified array.

  Output: -1

Implementation :
 

22 found at index = 3
p found at index = 3
3 found at index = 2
1.5 found at index = -2
35.0 found at index = -5
5 found at index = -1

Complexity Analysis:

Time Complexity:
The time complexity of the binarySearch() method in the Arrays class is O(log n) for searching within a specified range. In the given code, the binarySearch() method is called six times, each time with a different array and a different range of elements. Therefore, the time complexity of the entire code would be O(log n) * 6, which can be simplified to O(log n).

Auxiliary Space:
The binarySearch() method does not use any additional space. Therefore, the auxiliary space complexity of the code is O(1).

Exceptions :  

1. IllegalArgumentException : throws when starting index(fromIndex) is greater than the end index(toIndex) of specified range.(means: fromIndex > toIndex)
2. ArrayIndexOutOfBoundsException : throws if one or both index are not valid means fromIndex<0 or toIndex > arr.length.

Important Points:  

• If the input list is not sorted, the results are undefined.
• If there are duplicates, there is no guarantee which one will be found.

Reference : 

https://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html#binarySearch(int%5B%5D,%20int)