剑指 Offer 10- II. 青蛙跳台阶问题

class Solution {
public:
    int numWays(int n) 
    {    
        vector<int> v(n + 1, 1); 
        for(int i = 2; i <= n; i++)
            v[i] = (v[i - 1] + v[i - 2]) % 1000000007;
        return v[n];
    }
};