Binary search is the example of divide and conquer algorithm . This is best algorithm with running time of Log base 2 n . In this article we will see , how could we use this algorithm to insert an element in sorted list while marinating the sorted order of the list.
I got a mail asking,
“How we could insert an item in sorted generic list such that after insertion list would be remaining sorted?”
Answer of this is using Binary Search
As we know Binary search works on Divide and conquer algorithm. And running time using Binary search is very efficient.
So we need to follow below algorithm
Step 1
Sort the list
Step 2
Save the value to be inserted in a variable
Step 3
Do the binary search of the inserted variable in the list.
Step 4
Insert the item at the compliment of the number returned by the binary search.
Example #1 inserting a string in sorted list of string.
Program.cs
using System;
usingSystem.Collections.Generic;
usingSystem.Linq;
usingSystem.Text;
usingSystem.Collections.ObjectModel;
namespace ConsoleApplication21
{
classProgram
{
staticvoid Main(string[] args)
{
ListlstMyString = newList();
lstMyString.Add("Apple");
lstMyString.Add("Mango");
lstMyString.Add("Banana");
lstMyString.Add("papya ");
lstMyString.Sort();
foreach (var r inlstMyString)
{
Console.WriteLine(r);
}
Console.ReadKey(true);
}
}
}
Output
Now if in above sorted list we need to add one more string item cashew.
stringstrToInsert = "Cashew";
intbinraySearchIndex = lstMyString.BinarySearch(strToInsert);
if (binraySearchIndex< 0)
{
lstMyString.Insert(~binraySearchIndex, strToInsert);
}
So first we need to perform the binary search and then find the index of the next top element by negating the integer returned by the Binary search.
Program.cs
namespace ConsoleApplication21
{
classProgram
{
staticvoid Main(string[] args)
{
ListlstMyString = newList();
lstMyString.Add("Apple");
lstMyString.Add("Mango");
lstMyString.Add("Banana");
lstMyString.Add("papya ");
lstMyString.Sort();
stringstrToInsert = "Cashew";
intbinraySearchIndex = lstMyString.BinarySearch(strToInsert);
if (binraySearchIndex< 0)
{
lstMyString.Insert(~binraySearchIndex, strToInsert);
}
foreach (var r inlstMyString)
{
Console.WriteLine(r);
}
Console.ReadKey(true);
}
Ouput
Example #2: Inserting a custom class in list of custom class .
I have a class called Product
Product.cs
classProduct
{
publicstringProductName { get; set; }
publicintProductPrice { get; set; }
}
And List of Product as below,
List<Product>prdList = newList<Product>()
{
newProduct {ProductName = "Apple",ProductPrice = 101},
newProduct {ProductName = "Apple",ProductPrice = 99},
newProduct {ProductName = "Pen",ProductPrice = 99},
newProduct {ProductName = "Pencil", ProductPrice = 100},
newProduct {ProductName ="Apple", ProductPrice = 100},
newProduct { ProductName = "Mango", ProductPrice = 35},
newProduct {ProductName = "Shirt", ProductPrice=200}
} ;
Now first let us sort this list.
prdList.Sort(compare.Compare);
How to sort a Generic List? Read here
Now in sorted list of Product we need to insert one more product such that it should be inserted in sorted order in the list.
int search = 0;
ProductproductToInsert = new Product {
ProductName = "Ball",
ProductPrice = 30 };
search = prdList.BinarySearch(productToInsert, (IComparer<product>)compare);
if (search < 0)
{
prdList.Insert(~search, productToInsert);
}
Program.cs
using System;
usingSystem.Collections.Generic;
usingSystem.Linq;
usingSystem.Text;
usingSystem.Collections.ObjectModel;
namespace ConsoleApplication21
{
classProgram
{
staticvoid Main(string[] args)
{
inttempPrevious = 0;
inttempcurrent = 0;
IComparer compare = newCompareProduct();
List<Product>prdList = newList<Product>()
{
newProduct {ProductName = "Apple",ProductPrice = 101},
newProduct {ProductName = "Apple",ProductPrice = 99},
newProduct {ProductName = "Pen",ProductPrice = 99},
newProduct {ProductName = "Pencil", ProductPrice = 100},
newProduct {ProductName ="Apple", ProductPrice = 100},
newProduct { ProductName = "Mango", ProductPrice = 35},
newProduct {ProductName = "Shirt", ProductPrice=200}
} ;
prdList.Sort(compare.Compare);
int search = 0;
ProductproductToInsert = new Product {
ProductName = "Ball",
ProductPrice = 30 };
search = prdList.BinarySearch(productToInsert, (IComparer<product>)compare);
if (search < 0)
{
prdList.Insert(~search, productToInsert);
}
foreach (Productp inprdList)
{
tempcurrent = p.ProductPrice;
if (tempcurrent != tempPrevious)
{
Console.WriteLine("**********************");
Console.WriteLine("Price = " + p.ProductPrice);
}
Console.WriteLine(p.ProductName);
tempPrevious = p.ProductPrice;
}
Console.ReadKey(true);
}
}
Output
For reference generic sort class for list of Product is as below
classCompareProduct : IComparer
{
publicint Compare( Product p1, Product p2)
{
int result;
if (Product.ReferenceEquals(p1, p2))
{
result = 0;
}
else
{
if (p1 == null)
{
result = 1;
}
elseif (p2 == null)
{
result = -1;
}
else
{
result = NumberCompare(p1.ProductPrice, p2.ProductPrice);
//result = StringCompare(p1.ProductName, p2.ProductName);
if (result == 0)
{
// result = NumberCompare(p1.ProductPrice, p2.ProductPrice);
result = StringCompare(p1.ProductName, p2.ProductName);
}
}
}
return result;
}
intStringCompare(stringstrFirstString, stringsecondString)
{
int result;
if (strFirstString == null)
{
if (secondString == null)
{
result = 0;
}
else
{
result = 1;
}
}
else
{
result = strFirstString.CompareTo(secondString);
}
return result;
}
intNumberCompare(int number1, int number2)
{
int result;
if (number1 > number2)
{
result = 1;
}
elseif (number1 < number2)
{
result = -1;
}
else
{
result = 0;
}
return result;
}