Python/data_structures/binary_tree/fenwick_tree.py

from __future__ import print_function
class FenwickTree:

    def __init__(self, SIZE): # create fenwick tree with size SIZE
        self.Size = SIZE
        self.ft = [0 for i in range (0,SIZE)]

    def update(self, i, val): # update data (adding) in index i in O(lg N)
        while (i < self.Size):
            self.ft[i] += val
            i += i & (-i)

    def query(self, i): # query cumulative data from index 0 to i in O(lg N)
        ret = 0
        while (i > 0):
            ret += self.ft[i]
            i -= i & (-i)
        return ret

if __name__ == '__main__':
    f = FenwickTree(100)
    f.update(1,20)
    f.update(4,4)
    print(f.query(1))
    print(f.query(3))
    print(f.query(4))
    f.update(2,-5)
    print(f.query(1))
    print(f.query(3))