There are N steps.ur at the No.Y step.How many ways would it be if u walk K steps?one step once.
题目
There are N steps.ur at the No.Y step.How many ways would it be if u walk K steps?one step once.
There are N steps.ur at the No.Y step.How many ways would it be if u walk K steps?one step one time.Who's smart enough to help me solve this problem?Help please.
答案
It would be two ways---upstairs or downstairs.
两种情况：上楼、下楼.
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