CF1239A Ivan the Fool and the Probability Theory

思路：

可以转化为“strip”(http://tech-queries.blogspot.com/2011/07/fit-12-dominos-in-2n-strip.html)问题。参考了https://www.cnblogs.com/lyttt/p/11723194.html。

实现：

 #include <bits/stdc++.h>
 using namespace std;
 const int MOD = 1e9 + ;
 int a[];
 int main()
 {
     a[] = ; a[] = ;
     for (int i = ; i <= ; i++) a[i] = (a[i - ] + a[i - ]) % MOD;
     int n, m;
     while (cin >> n >> m)
     {
         cout << (a[n] + a[m] - ) % MOD *  % MOD << endl;
     }
     return ;
 }