易知 f(n)=f(n-1)+f(n-2)+……f(1)+1f(n-1)=f(n-2)+……f(1)+1两式相减得f(n)=2f(n-1),同时应该考虑n=1的情况 public class Solution { public int JumpFloorII(int target) { return target<1?0:(target==1?1:1<<(target-1)); } }