Leetcode70.爬楼梯

class Solution {
public:
    int climbStairs(int n) {
        if(n==1) return 1;
        if(n==2) return 2;
        int dp[n+1];
        dp[1]=1;dp[2]=2;
        for(int i=3;i<=n;++i){
            dp[i] = dp[i-1] + dp[i-2];
        }
        return dp[n];
    }
};