feat: add Fenwick Tree Data Structure using Java

Data Structures/FenwickTree/FenwickTree.java

@@ -0,0 +1,64 @@
+import java.util.Scanner;
+
+public class FenwickTree {
+
+    private void update(int[] arr, int pos, int val) {
+        int len = arr.length;
+        for (; pos < len; pos |= (pos + 1)) {
+            arr[pos] += val;
+        }
+    }
+
+    private int query(int[] arr, int pos) {
+        int sum = 0;
+        for (; pos >= 0; pos = (pos & (pos + 1)) - 1) {
+            sum += arr[pos];
+        }
+
+        return sum;
+    }
+
+    public static void main(String[] args) {
+        Scanner scan = new Scanner(System.in);
+        System.out.println("Fenwick Tree Test\n");
+
+        // Accept number of elements
+        System.out.println("Enter number of integer elements");
+        int n = scan.nextInt();
+
+        // Create integer array on n elements
+        int arr[] = new int[n];
+
+        FenwickTree ft = new FenwickTree();
+
+        // Update or find sum
+        char ch;
+        do {
+            System.out.println("\nFenwick Tree Operations\n");
+            System.out.println("1. update ");
+            System.out.println("2. query");
+
+            int choice = scan.nextInt();
+            switch (choice) {
+                case 1:
+                    System.out.println("Enter position and value to update");
+                    ft.update(arr, scan.nextInt(), scan.nextInt());
+                    break;
+                case 2: 
+                    System.out.println("Enter position to find sum till nth element");
+                    try {
+                        System.out.println("Sum = "+ ft.query(arr, scan.nextInt()));
+                    } catch (Exception e) {
+                        System.out.println("\nError! Out of bounds\n");
+                    }
+                    break;
+            default: 
+                System.out.println("Wrong Entry \n ");
+                break;
+            }
+
+            System.out.println("\nDo you want to continue (Type y or n)\n");
+            ch = scan.next().charAt(0);
+        } while (ch == 'Y'|| ch == 'y');
+    }
+}