JAVA

java Difference Array | Range update query in O(1)

// Java code to demonstrate Difference Array
class GFG {
     
    // Creates a diff array D[] for A[] and returns
    // it after filling initial values.
    static void initializeDiffArray(int A[], int D[])
    {
         
        int n = A.length;
 
        D[0] = A[0];
        D[n] = 0;
        for (int i = 1; i < n; i++)
            D[i] = A[i] - A[i - 1];
    }
 
    // Does range update
    static void update(int D[], int l, int r, int x)
    {
        D[l] += x;
        D[r + 1] -= x;
    }
 
    // Prints updated Array
    static int printArray(int A[], int D[])
    {
        for (int i = 0; i < A.length; i++) {
             
            if (i == 0)
                A[i] = D[i];
 
            // Note that A[0] or D[0] decides
            // values of rest of the elements.
            else
                A[i] = D[i] + A[i - 1];
 
            System.out.print(A[i] + " ");
        }
         
        System.out.println();
         
        return 0;
    }
     
    // Driver Code
    public static void main(String[] args)
    {
        // Array to be updated
        int A[] = { 10, 5, 20, 40 };
        int n = A.length;
        // Create and fill difference Array
        // We use one extra space because
        // update(l, r, x) updates D[r+1]
        int D[] = new int[n + 1];
        initializeDiffArray(A, D);
 
        // After below update(l, r, x), the
        // elements should become 20, 15, 20, 40
        update(D, 0, 1, 10);
        printArray(A, D);
 
        // After below updates, the
        // array should become 30, 35, 70, 60
        update(D, 1, 3, 20);
        update(D, 2, 2, 30);
         
        printArray(A, D);
    }
}
 
// This code is contributed by Anant Agarwal.