1111...=2^n-1长度为n的都是1的二进制数=2的n次方-1思路：对于每个数只有选或不选（1或0）的二进制，剩余见代码点击查看代码#include<bits/stdc++.h>usingnamespacestd;longlongf[20];intmain(){ freopen("202409C.in","r",stdin); freopen("202409C.out