70. Climbing Stairs

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) {
        /* recursive
        if(n<=0) return 0;
        else if(n==1) return 1;
        else if(n==2) return 2;
        else return  climbStairs(n-1) + climbStairs(n-2);
        */
        if(n <= 0) return 0;
        vector<int> v = vector<int>();
        v.push_back(1);
        v.push_back(2);
        while(v.size() < n) v.push_back(v[v.size()-1] + v[v.size()-2]);
        return v[n-1];
    }
};