A frog can jump up to one or two steps at a time. Find the total number of jumping methods the frog jumps on an n-level step.
The answer needs to be modulo 1e9+7 (1000000007). If the initial result of the calculation is: 1000000008, please return 1.
Example 1:
输入：n = 2
输出：2
Example 2:
输入：n = 7
输出：21
Example 3:
输入：n = 0
输出：1
prompt:
0 <= n <= 100
Note: This question is the same as the 70 question on the main site: https://leetcode-cn.com/problems/climbing-stairs/
Dynamic programming
f(x) = f(x - 1) + f(x - 2)
Idea reference: https://blog.csdn.net/qq_30457077/article/details/114276198
class Solution {
public:
int numWays(int n) {
int p = 0, q = 0, r = 1;//初始化p为0 q为f(0)==0 r为f(1)==1
//p q r分别指f(x - 2) f(x - 1) f(x)
for (int i = 1; i <= n; ++i) {
p = q;
q = r;
r = (p + q) % 1000000007;
}
return r;
}
};