leetcode---climbing-stairs---dp

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?

class Solution {public:    int climbStairs(int n)     {        if(n == 0)            return 0;        vector<int> dp(n+1, 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];    }};