gistfile1.py

def fill(heights):
    prev = total = 0
    for i, h in enumerate(heights):
        f = min(max(heights[i:]), prev)
        if f > h:
            total += (f - h)
        prev = max(prev, h)
    return total

if __name__ == "__main__":
    print fill((2,5,1,2,3,4,7,7,6))
    print fill((2,5,1,3,1,2,1,7,0,0))