3
Need help for this combinatorics problem
source link: http://codeforces.com/blog/entry/104573
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You are given two types of people, type A and type B. You need to place n people of any type but the condition is that no two A type people is close to each other, means [A,A,B,A,B] not possible since two A type person are close to each other. You need to find all the possible arrangement. Print the answer modulo 1e9 + 7.
Constraints
1 <= n <= 100000
Input: 3 Output: 5
Explanation: if n = 3 then possible combinations are [B,B,B] [A,B,B] [B,A,B] [B,B,A] [A,B,A]
So the answer is 5.
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