How many ways are there to to climb n steps (recurrence relations)?

In summary, the conversation discusses the number of ways to climb a set of steps, represented by ##n##, given that the first step has already been climbed. The equations provided, ##s_n=s_{n-1}## and ##s_n=s_{n-2}##, are incorrect as they do not accurately represent the number of ways to climb ##n## steps. The correct recurrence relation is discussed under "Relevant Equations."
  • #1
Eclair_de_XII
1,083
91
Homework Statement
Tom wants to climb ##n## steps. He can either climb one step at a time, or two steps at a time.
(a) How many ways are there for him to climb ##n## steps if he initially takes one step?
(b) How many ways are there if he initially takes two steps?
(c) Use these two answers in order to derive a recurrence relation for ##s_n##, the number of ways to climb ##n## steps.
Relevant Equations
The answer to (c) as Google-searched: ##s_n=s_{n-1}+s_{n-2}##.
(a) Okay, so if Tom climbs the first step, then he has ##n-1## steps to climb. So the number of ways to climb ##n## steps given he has initially climbed one, is ##s_n=s_{n-1}##.
(b) Similarly, ##s_n=s_{n-2}##.
 
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  • #2
The words you have written are correct but the equations are not. ##s_n## represents the number of ways to climb n steps, not the number of ways to climb n steps when the first step is 1, nor the number of ways to climb n steps when the first step is 2. So you need to delete the characters "##s_n=##" from your answers.

The recurrence relation is what you have already written under 'Relevant Equations'.
 
  • #3
So I just add the two answers togther?
 
  • #4
Err, how do you mark this thread as "solved"?
 

Related to How many ways are there to to climb n steps (recurrence relations)?

1. How do you calculate the number of ways to climb n steps using recurrence relations?

The number of ways to climb n steps using recurrence relations can be calculated by using the formula: f(n) = f(n-1) + f(n-2) + f(n-3) + ... + f(n-k), where k is the maximum number of steps that can be taken in one move. This formula is based on the idea that the number of ways to reach the nth step is equal to the sum of the number of ways to reach the previous steps.

2. What is the base case in recurrence relations for climbing n steps?

The base case in recurrence relations for climbing n steps is f(0) = 1, which means there is only one way to climb 0 steps (by not taking any steps).

3. How does the time complexity of calculating the number of ways to climb n steps using recurrence relations compare to other methods?

The time complexity of calculating the number of ways to climb n steps using recurrence relations is O(nk), where n is the number of steps and k is the maximum number of steps that can be taken in one move. This is more efficient than other methods, such as brute force, which has a time complexity of O(2^n).

4. Can recurrence relations be used to solve other types of problems besides climbing n steps?

Yes, recurrence relations can be used to solve a variety of problems in mathematics and computer science, such as calculating Fibonacci numbers, finding the shortest path in a graph, and determining the number of ways to arrange objects in a certain pattern.

5. Are there any limitations to using recurrence relations for solving problems?

One limitation of using recurrence relations is that it may not always be the most efficient method for solving a problem. In some cases, other approaches, such as dynamic programming, may be more suitable. Additionally, the time complexity of recurrence relations can increase significantly if the problem involves a large number of steps or has a complex recurrence formula.

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