70. Climbing Stairs爬楼梯问题

1.问题描述

You are climbing a stair case. It takes n steps to reach to the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

在爬楼梯时，每次可向上走1阶台阶或2阶台阶，问有n阶楼梯有多少种上楼的方式？

C++

class Solution {
public:
    int climbStairs(int n) {
        vector<int> dp(n+3, 0);
        dp[1] = 1;
        dp[2] = 2;
        for(int i=3; i<=n; i++) {
            dp[i] = dp[i-1] + dp[i-2];
        }
        return dp[n];
    }
};