codeforces 792D - Paths in a Complete Binary Tree

 #include<cstdio>
 #include<iostream>
 #define lowbit(x) x&(-x)
 typedef long long ll;
 using namespace std;
 ll n,q,num,root;string s;
 int main()
 {
     scanf("%I64d%I64d",&n,&q);
     root=(n+)/;
     for(ll q_i=;q_i<=q;q_i++)
     {
         cin>>num>>s;
         for(int step=;step<s.size();step++)
         {
             ll lowbit_num=lowbit(num);//假设num这个节点是左子节点
             if(s[step]=='U' && num!=root)
             {
                 ll num_u=num+lowbit_num;//求出在假设情况下的num的父节点num_u
                 ll lowbit_num_u=lowbit(num_u);
                 if(num_u - lowbit_num_u/ == num) num=num_u;//如果根据父节点求出来的左孩子就是num，那么num确实是左子节点
                 else num=num-lowbit_num;//否则num就是右子节点
             }
             if(s[step]=='L') num-=lowbit_num/;
             if(s[step]=='R') num+=lowbit_num/;
         }
         printf("%I64d\n",num);
     }
 }

思路来自http://blog.csdn.net/Courage_kn/article/details/69218592

用#define比定义一个lowbit函数快……不过好像很多时候不能像函数那样随便用，容易出问题……

这是分别用

long long lowbit(long long x){return x&(-x);}

和

#define lowbit(x) x&(-x)

情况下的耗时……