题目：
解题思路：
动态规划
https://leetcode-cn.com/problems/climbing-stairs/solution/pa-lou-ti-by-leetcode-solution/
代码：
class Solution {
public int climbStairs(int n) {
int p = 0, q = 0, r = 1;
for (int i = 1; i <= n; ++i) {
p = q;
q = r;
r = p + q;
}
return r;
}
}
