Binary Indexed Tree : Range Updates and Point Queries

// C# program to demonstrate Range Update 
// and Point Queries Without using BIT 
using System;

class GfG 
{ 

// Updates such that getElement() 
// gets an increased value when
// queried from l to r. 
static void update(int []arr, int l, 
                    int r, int val) 
{ 
    arr[l] += val; 
    if(r + 1 < arr.Length) 
    arr[r + 1] -= val; 
} 

// Get the element indexed at i 
static int getElement(int []arr, int i) 
{ 
    // To get ith element sum of all the elements 
    // from 0 to i need to be computed 
    int res = 0; 
    for (int j = 0 ; j <= i; j++) 
        res += arr[j]; 

    return res; 
} 

// Driver code 
public static void Main(String[] args) 
{ 
    int []arr = {0, 0, 0, 0, 0}; 
    int n = arr.Length; 

    int l = 2, r = 4, val = 2; 
    update(arr, l, r, val); 

    //Find the element at Index 4 
    int index = 4; 
    Console.WriteLine("Element at index " + 
                        index + " is " +
                        getElement(arr, index)); 

    l = 0; 
    r = 3; 
    val = 4; 
    update(arr,l,r,val); 

    //Find the element at Index 3 
    index = 3; 
    Console.WriteLine("Element at index " + 
                            index + " is " +
                            getElement(arr, index)); 
} 
} 

// This code is contributed by PrinciRaj1992

using System;

/* C# code to demonstrate Range Update and 
* Point Queries on a Binary Index Tree. 
* This method only works when all array 
* values are initially 0.*/
public class GFG
{

    // Max tree size 
    public const int MAX = 1000;

    public static int[] BITree = new int[MAX];

    // Updates a node in Binary Index 
    // Tree (BITree) at given index 
    // in BITree. The given value 'val' 
    // is added to BITree[i] and 
    // all of its ancestors in tree. 
    public static void updateBIT(int n, int index, int val)
    {
        // index in BITree[] is 1  
        // more than the index in arr[] 
        index = index + 1;

        // Traverse all ancestors  
        // and add 'val' 
        while (index <= n)
        {
            // Add 'val' to current  
            // node of BITree 
            BITree[index] += val;

            // Update index to that  
            // of parent in update View 
            index += index & (-index);
        }
    }

    // Constructs Binary Indexed Tree  
    // for given array of size n. 

    public static void constructBITree(int[] arr, int n)
    {
        // Initialize BITree[] as 0 
        for (int i = 1; i <= n; i++)
        {
            BITree[i] = 0;
        }

        // Store the actual values  
        // in BITree[] using update() 
        for (int i = 0; i < n; i++)
        {
            updateBIT(n, i, arr[i]);
        }

        // Uncomment below lines to  
        // see contents of BITree[] 
        // for (int i=1; i<=n; i++) 
        //     cout << BITree[i] << " "; 
    }

    // SERVES THE PURPOSE OF getElement() 
    // Returns sum of arr[0..index]. This  
    // function assumes that the array is 
    // preprocessed and partial sums of 
    // array elements are stored in BITree[] 
    public static int getSum(int index)
    {
        int sum = 0; //Initialize result

        // index in BITree[] is 1 more  
        // than the index in arr[] 
        index = index + 1;

        // Traverse ancestors 
        // of BITree[index] 
        while (index > 0)
        {

            // Add current element  
            // of BITree to sum 
            sum += BITree[index];

            // Move index to parent  
            // node in getSum View 
            index -= index & (-index);
        }

        // Return the sum 
        return sum;
    }

    // Updates such that getElement()  
    // gets an increased value when  
    // queried from l to r. 
    public static void update(int l, int r, int n, int val)
    {
        // Increase value at  
        // 'l' by 'val' 
        updateBIT(n, l, val);

        // Decrease value at 
        // 'r+1' by 'val' 
        updateBIT(n, r + 1, -val);
    }


    // Driver Code 
    public static void Main(string[] args)
    {
        int[] arr = new int[] {0, 0, 0, 0, 0};
        int n = arr.Length;

        constructBITree(arr,n);

        // Add 2 to all the 
        // element from [2,4] 
        int l = 2, r = 4, val = 2;
        update(l, r, n, val);

        int index = 4;

        Console.WriteLine("Element at index " + index + " is " + getSum(index));

        // Add 2 to all the  
        // element from [0,3] 
        l = 0;
        r = 3;
        val = 4;
        update(l, r, n, val);

        // Find the element 
        // at Index 3 
        index = 3;
        Console.WriteLine("Element at index " + index + " is " + getSum(index));
    }
}


  // This code is contributed by Shrikant13