跳台阶

class Solution {
public:
    int jumpFloor(int number) {
        // f(0) = 0
        // f(1) = 1
        // f(2) = 2
        // ...
        // f(n-2) = f(n-3) + f(n-4)
        // f(n-1) = f(n-2) + f(n-3)
        // f(n)   = f(n-1) + f(n-2)
        
        if(number <= 0) return 0;
        if(number == 1) return 1;
        if(number == 2) return 2;
        
        int small = 1;
        int large = 2;
        int ret = 0;
        
        for(int i = 0; i < number - 2; i++)
        {
            ret = large + small;
            small = large;
            large = ret;
        }
        return ret;
    }
};