#3154

Find Number of Ways to Reach the K-th Stair

hard · 37.5% accepted · 194 likes · top 16%

math · dynamic programming · bit manipulation · memoization · combinatorics

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Description

You are given a non-negative integer k. There exists a staircase with an infinite number of stairs, with the lowest stair numbered 0.

Alice has an integer jump, with an initial value of 0. She starts on stair 1 and wants to reach stair k using any number of operations. If she is on stair i, in one operation she can:

- Go down to stair i - 1. This operation cannot be used consecutively or on stair 0.

- Go up to stair i + 2jump. And then, jump becomes jump + 1.

Return the total number of ways Alice can reach stair k.

Note that it is possible that Alice reaches the stair k, and performs some operations to reach the stair k again.

Solution