test_tree.py

def tree(p):
    n = len(p) + 1
    g = [0.] * (n-1)
    h = [0.] * (n-1)
    i = n - 2
    while i >= 0:
        l = 2 * i + 1
        r = 2 * i + 2
        if l >= n - 1:
            g[i] = p[l - n]
        else:
            g[i] = g[l] + h[l]
        if r >= n - 1:
            h[i] = p[r - n]
        else:
            h[i] = g[r] + h[r]
        i -= 1
    return g, h