question:
The largest item in a heap must appear in position 1, and the second largest must be in the position 2 or position 3. Give the list of positions in a heap of size 31 where the kth largest (i) can apprar, and (ii) cannot appear, for k = 2, 3, 4 (assuming the values to be distinct).
answer:
第k大的可以出现在 （第log2 k 向下取整） 到 {（第log2 k 向下取整） + [2^（第log2 k 向下取整）] - 1}，（左右闭区间）