How to use Array.BinarySearch() Method in C# | Set 1 (original) (raw)

Last Updated : 18 Aug, 2023

Array.BinarySearch() method is used to search a value in a sorted one dimensional array. The binary search algorithm is used by this method. This algorithm searches a sorted array by repeatedly dividing the search interval in half. Begin with an interval covering the whole array. If the value of the search key is less than the item in the middle of the interval, narrow the interval to the lower half. Otherwise, narrow it to the upper half. Repeatedly check until the value is found or the interval is empty.

Important Points:

There are total 8 methods in the overload list of this method as follows:

BinarySearch(Array, Object) Method

This method is used to search a specific element in the entire 1-D sorted array. It used the IComparable interface that is implemented by each element of the 1-D array and the specified object. This method is an O(log n) operation, where n is the Length of the specified array.

Syntax: public static int BinarySearch (Array arr, object val);
Parameters:
arr: It is the sorted 1-D array to search.
val: It is the object to search for.

Return Value: It returns the index of the specified _val_in the specified arr if the val is found otherwise it returns a negative number. There are different cases of return values as follows:

Exceptions:

Below programs illustrate the above-discussed method:

Example 1:

C# `

// C# program to illustrate the // Array.BinarySearch(Array, Object) // Method using System;

class GFG {

// Main Method
public static void Main(String[] args)
{

    // taking an 1-D Array
    int[] arr = new int[7] { 1, 5, 7, 4, 6, 2, 3 };

    // for this method array
    // must be sorted
    Array.Sort(arr);

    Console.Write("The elements of Sorted Array: ");

    // calling the method to
    // print the values
    display(arr);

    // taking the element which is
    // to search for in a variable
    // It is not present in the array
    object s = 8;

    // calling the method containing
    // BinarySearch method
    result(arr, s);

    // taking the element which is
    // to search for in a variable
    // It is present in the array
    object s1 = 4;

    // calling the method containing
    // BinarySearch method
    result(arr, s1);
}

// containing BinarySearch Method
static void result(int[] arr2, object k)
{

    // using the method
    int res = Array.BinarySearch(arr2, k);

    if (res < 0) {
        Console.WriteLine("\nThe element to search for "
                              + "({0}) is not found.",
                          k);
    }

    else {
        Console.WriteLine("The element to search for "
                              + "({0}) is at index {1}.",
                          k, res);
    }
}

// display method
static void display(int[] arr1)
{

    // Displaying Elements of array
    foreach(int i in arr1)
        Console.Write(i + " ");
}

}

`

Output:

The elements of Sorted Array: 1 2 3 4 5 6 7 The element to search for (8) is not found. The element to search for (4) is at index 3.

Example 2:

C# `

// C# program to illustrate the // Array.BinarySearch(Array, Object) // Method using System;

class GFG {

// Main Method
public static void Main(String[] args)
{

    // taking an 1-D Array
    int[] arr = new int[7] { 1, 5, 7, 4, 6, 2, 3 };

    // for this method array
    // must be sorted
    Array.Sort(arr);

    Console.Write("The elements of Sorted Array: ");

    // calling the method to
    // print the values
    display(arr);

    // it will return a negative value as
    // 9 is not present in the array
    Console.WriteLine("\nIndex of 9 is: " + Array.BinarySearch(arr, 9));
}

// display method
static void display(int[] arr1)
{

    // Displaying Elements of array
    foreach(int i in arr1)
        Console.Write(i + " ");
}

}

`

Output:

The elements of Sorted Array: 1 2 3 4 5 6 7 Index of 9 is: -8

BinarySearch(Array, Object, IComparer) Method

This method is used to search a specific element in the entire 1-D sorted array using the specified IComparer interface.

Syntax: public static int BinarySearch(Array arr, Object val, IComparer comparer)
Parameters:
arr : The one-dimensional sorted array in which the search will happen.
val : The object value which is to search for.
comparer : When comparing elements then the IComparer implementation is used.

Return Value: It returns the index of the specified val in the specified arr if the val is found otherwise it returns a negative number. There are different cases of return values as follows:

Exceptions:

Example:

C# `

// C# program to demonstrate the // Array.BinarySearch(Array, // Object, IComparer) Method using System;

class GFG {

// Main Method
public static void Main()
{

    // initializes a new Array.
    Array arr = Array.CreateInstance(typeof(Int32), 5);

    // Array elements
    arr.SetValue(20, 0);
    arr.SetValue(10, 1);
    arr.SetValue(30, 2);
    arr.SetValue(40, 3);
    arr.SetValue(50, 4);

    Console.WriteLine("The original Array");

    // calling "display" function
    display(arr);

    Console.WriteLine("\nsorted array");

    // sorting the Array
    Array.Sort(arr);

    display(arr);

    Console.WriteLine("\n1st call");

    // search for object 10
    object obj1 = 10;

    // call the "FindObj" function
    FindObj(arr, obj1);

    Console.WriteLine("\n2nd call");
    object obj2 = 60;
    FindObj(arr, obj2);
}

// find object method
public static void FindObj(Array Arr,
                           object Obj)
{
    int index = Array.BinarySearch(Arr, Obj,
                                   StringComparer.CurrentCulture);

    if (index < 0) {
        Console.WriteLine("The object {0} is not found\nNext"
                              + " larger object is at index {1}",
                          Obj, ~index);
    }
    else {
        Console.WriteLine("The object {0} is at index {1}",
                          Obj, index);
    }
}

// display method
public static void display(Array arr)
{
    foreach(int g in arr)
    {
        Console.WriteLine(g);
    }
}

}

`

Output:

The original Array 20 10 30 40 50

sorted array 10 20 30 40 50

1st call The object 10 is at index 0

2nd call The object 60 is not found Next larger object is at index 5

BinarySearch(Array, Int32, Int32, Object) Method

This method is used to search a value in the range of elements in a 1-D sorted array. It uses the IComparable interface implemented by each element of the array and the specified value. It searches only in a specified boundary which is defined by the user.

Syntax: public static int BinarySearch(Array arr, int i, int len, object val);
Parameters:
arr: It is 1-D array in which the user have to search for an element.
i: It is the starting index of the range from where the user want to start the search.
len: It is the length of the range in which the user want to search.
val: It is the value which the user to search for.

Return Value: It returns the index of the specified val in the specified arr if the val is found otherwise it returns a negative number. There are different cases of return values as follows:

Exceptions:

Example:

C# `

// C# Program to illustrate the use of // Array.BinarySearch(Array, Int32, // Int32, Object) Method using System; using System.IO;

class GFG {

// Main Method
static void Main()
{
    // initializing the integer array
    int[] intArr = { 42, 5, 7, 12, 56, 1, 32 };

    // sorts the intArray as it must be
    // sorted before using method
    Array.Sort(intArr);

    // printing the sorted array
    foreach(int i in intArr) Console.Write(i + " "
                                           + "\n");

    // intArr is the array we want to find
    // and 1 is the starting index
    // of the range to search. 5 is the
    // length of the range to search.
    // 32 is the object to search
    int index = Array.BinarySearch(intArr, 1, 5, 32);

    if (index >= 0) {

        // if the element is found it
        // returns the index of the element
        Console.WriteLine("Index of 32 is : " + index);
    }

    else {

        // if the element is not
        // present in the array or
        // if it is not in the
        // specified range it prints this
        Console.Write("Element is not found");
    }

    // intArr is the array we want to
    // find. and 1 is the starting
    // index of the range to search. 5 is
    // the length of the range to search
    // 44 is the object to search
    int index1 = Array.BinarySearch(intArr, 1, 5, 44);

    // as the element is not present
    // it prints a negative value.
    Console.WriteLine("Index of 44 is :" + index1);
}

}

`

Output:

1 5 7 12 32 42 56 Index of 32 is : 4 Index of 44 is :-7

BinarySearch(Array, Int32, Int32, Object, IComparer) Method

This method is used to search a value in the range of elements in a 1-D sorted array using a specified IComparer interface.

Syntax: public static int BinarySearch(Array arr, int index, int length, Object value, IComparer comparer)
Parameters:
arr : The sorted one-dimensional Array which is to be searched.
index : The starting index of the range from which searching will start.
length : The length of the range in which the search will happen.
value : The object to search for.
comparer : When comparing elements then use the IComparer implementation.

Return Value: It returns the index of the specified value in the specified arr, if the value is found otherwise it returns a negative number. There are different cases of return values as follows:

Example: In this example, here we use "CreateInstance()" method to create a typed array and stores some integer value and search some values after sort the array.

C# `

// C# program to demonstrate the // Array.BinarySearch(Array, // Int32, Int32, Object, // IComparer) Method using System;

class GFG {

// Main Method
public static void Main()
{
    // initializes a new Array.
    Array arr = Array.CreateInstance(typeof(Int32), 8);

    // Array elements
    arr.SetValue(20, 0);
    arr.SetValue(10, 1);
    arr.SetValue(30, 2);
    arr.SetValue(40, 3);
    arr.SetValue(50, 4);
    arr.SetValue(80, 5);
    arr.SetValue(70, 6);
    arr.SetValue(60, 7);

    Console.WriteLine("The original Array");

    // calling "display" function
    display(arr);

    Console.WriteLine("\nsorted array");

    // sorting the Array
    Array.Sort(arr);

    display(arr);

    Console.WriteLine("\n1st call");

    // search for object 10
    object obj1 = 10;

    // call the "FindObj" function
    FindObj(arr, obj1);

    Console.WriteLine("\n2nd call");
    object obj2 = 60;
    FindObj(arr, obj2);
}

// find object method
public static void FindObj(Array Arr,
                           object Obj)
{
    int index = Array.BinarySearch(Arr, 1, 4,
                                   Obj, StringComparer.CurrentCulture);

    if (index < 0) {
        Console.WriteLine("The object {0} is not found\n"
                              + "Next larger object is at index {1}",
                          Obj, ~index);
    }
    else {
        Console.WriteLine("The object {0} is at "
                              + "index {1}",
                          Obj, index);
    }
}

// display method
public static void display(Array arr)
{
    foreach(int g in arr)
    {
        Console.WriteLine(g);
    }
}

}

`

Output:

The original Array 20 10 30 40 50 80 70 60

sorted array 10 20 30 40 50 60 70 80

1st call The object 10 is not found Next larger object is at index 1

2nd call The object 60 is not found Next larger object is at index 5