两个数解决

public class Solution {
    public int JumpFloor(int target) {
        if(target < 1){
            return 0;
        }
        if(target < 3){
            return target;
        }
        /**
        1: 1
        2: 2
        3: 1 + 2 = 3;
        */
        int a = 1;
        int b = 2;
        for(int i = 3; i <= target; i++){
            b = a + b;
            a = b - a;
        }
        return b;
    }
}