interviewprob.py

class Tree:
    def __init__(self, x=0, l=None, r=None):
        self.x = x
        self.l = l
        self.r = r

def visibleCountRecursive(root, maxthusfar):
    visible = 0
    visibleLeft = 0
    visibleRight = 0

    if root.x >= maxthusfar:
        visible = 1

    if root.l is not None:
        visibleLeft = visibleCountRecursive(root.l, max(maxthusfar, root.x))

    if root.r is not None:
        visibleRight = visibleCountRecursive(root.r, max(maxthusfar, root.x))

    return visible + visibleLeft + visibleRight

def solution(root):
    return visibleCountRecursive(root, -1)

firstExample = Tree(5, Tree(3, Tree(20), Tree(21)), Tree(10, Tree(1), None))
secondExample = Tree(8, Tree(2, Tree(8), Tree(7)), Tree(6))

print solution(firstExample)
print solution(secondExample)