bzoj 2115: [Wc2011] Xor

 神题%%%

可以证明的是从1到n的路径是由一条路上挂着几个环构成的。

求出所有的环，线性基，最大，完了。

#include<bits/stdc++.h>
#define N 100005
#define LL long long
#define inf 0x3f3f3f3f
using namespace std;
inline LL ra()
{
    LL x=0,f=1; char ch=getchar();
    while (ch<'0' || ch>'9') {if (ch=='-') f=-1; ch=getchar();}
    while (ch>='0' && ch<='9') {x=x*10+ch-'0'; ch=getchar();}
    return x*f;
}
struct node{int to,next; LL v;}e[N<<2];
bool vis[N];
LL p[105],A[N<<2],dis[N];
int cnt,head[N],sz,n,m;
void insert(int x, int y, LL v)
{
    e[++cnt].to=y; e[cnt].next=head[x]; e[cnt].v=v; head[x]=cnt;
}
void dfs(int x, LL s)
{
    vis[x]=1; dis[x]=s;
    for (int i=head[x];i;i=e[i].next)
    {
        if (vis[e[i].to]) A[++sz]=e[i].v^s^dis[e[i].to];
        else dfs(e[i].to,s^e[i].v);
    }
}
void guass()
{
    for (int i=1; i<=sz; i++)
    {
        for (int j=62; j>=0; j--)
            if ((1LL<<j)&A[i])
            {
                if (!p[j]) {p[j]=A[i]; break;}
                else A[i]^=p[j];
            }
    }
}
int main()
{
    n=ra(); m=ra();
    for (int i=1; i<=m; i++) 
    {
        int x=(int)ra(),y=(int)ra(); LL v=ra();
        insert(x,y,v); insert(y,x,v);
    }
    dfs(1,0);
    guass();
    LL ans=dis[n];
    for (int i=62; i>=0; i--) ans=max(ans,ans^p[i]);
    cout<<ans<<endl;
    return 0;
}