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Count ways to reach the n'th stair
Medium Accuracy: 42.67% Submissions: 11753 Points: 4

There are N stairs, a person standing at the bottom wants to reach the top. The person can climb either 1 stair or 2 stairs at a time. Count the number of ways, the person can reach the top (order does matter).

Example 1:

Input:
N = 4
Output: 5
Explanation: You can reach 4th stair in
5 ways.

Example 2:

Input:
N = 10
Output: 89

Your Task:
Complete the function countWays() which takes the top stair number m as input parameters and returns the answer % 10^9+7.

Expected Time Complexity : O(N)
Expected Auxiliary Space: O(1)

Constraints:
1 <= N <= 105

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Count ways to reach the n'th stair

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