算法:跳台阶

public class Solution {
    public int JumpFloor(int n) {
        if (n <= 0) return 0;
        if (n <= 2) return n;
        int f1 = 1, f2 = 2;
        for (int i = 3; i <= n; ++i) {
            int temp = f2;
            f2 += f1;
            f1 = temp;
        }
        return f2;
    }
}