class Solution {
public:
    int climbStairs(int n) {
        if(n < 3)
            return n;
        int *arr = new int[n+1];
        arr[1] = 1;
        arr[2] = 2;
        for(int i = 3; i<=n; i++){
            arr[i] = arr[i-1] + arr[i-2];
        }
        int tmp =  arr[n];
        delete []arr;
        return tmp;
    }
};

class Solution {
public:
    int climbStairs(int n) {
        if(n < 3)
            return n;
        int t1 = 1;
        int t2 = 2;
        int tmp = 0;
        for(int i=3; i<=n; i++){
            tmp = t1 + t2;
            t1 = t2;
            t2 = tmp;
        }
        return tmp;
    }
};