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) {        if(n <=2)            return n;                vector<int> f(n,0);        f[0] = 1;        f[1] = 2;                for(int i = 2;i<n;i++)            f[i] = f[i-1] + f[i-2];        return f[n-1];            }};