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) { int n_1 = 1, n_2 = 1; int res = 1; for(int i=2;i<=n;i++) { res = n_1 + n_2; n_2 = n_1; n_1 = res; } return res; } };