package DataStructures.Trees;

public class FenwickTree {
    private int n;
    private int fen_t[];
    
    /* Constructor which takes the size of the array as a parameter */
    public FenwickTree(int n) {
        this.n = n;
        this.fen_t = new int[n + 1];
    }
    
    /* A function which will add the element val at index i*/
    public void update(int i, int val) {
        // As index starts from 0, increment the index by 1
        i += 1;
        while (i <= n) {
            fen_t[i] += val;
            i += i & (-i);
        }
    }
    
    /* A function which will return the cumulative sum from index 1 to index i*/
    public int query(int i) {
        // As index starts from 0, increment the index by 1
        i += 1;
        int cumSum = 0;
        while (i > 0) {
            cumSum += fen_t[i];
            i -= i & (-i);
        }
        return cumSum;
    }
}