CF 959 E. Mahmoud and Ehab and the xor-MST

E. Mahmoud and Ehab and the xor-MST

https://codeforces.com/contest/959/problem/E

分析：

　　每个点x应该和x ^ lowbit(x)连边，那么现在就是求$sum_{i=1}^{n}lowbit(i)$，然后打表找规律。

代码：

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>
#include<cmath>
#include<cctype>
#include<set>
#include<queue>
#include<vector>
#include<map>
using namespace std;
typedef long long LL;

inline int read() {
    int x=0,f=1;char ch=getchar();for(;!isdigit(ch);ch=getchar())if(ch=='-')f=-1;
    for(;isdigit(ch);ch=getchar())x=x*10+ch-'0';return x*f;
}

int main() {
    LL n, res = 0;
    cin >> n; n--;
    for (LL x = 1; x <= n; x <<= 1) 
        res += ((n - x) / (x + x) + 1) * x;
    cout << res;
    return 0;
}