bzoj 2115: [Wc2011] Xor xor高斯消元

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<set>
using namespace std;
#define MAXN 51000
#define MAXV 51000
#define MAXL 1000000
#define MAXE MAXV*4
typedef long long qword;
struct Edge
{
        int np;
        qword val;
        Edge *next;
}E[MAXE],*V[MAXV];
int tope=-1;
void addedge(int x,int y,qword z)
{
        E[++tope].np=y;
        E[tope].val=z;
        E[tope].next=V[x];
        V[x]=&E[tope];
}
bool vis[MAXN];
qword path_val[MAXN];
qword vec[MAXL];
int totv=0;
set<qword> S;
void dfs(int now,qword pv)
{
        Edge *ne;
        path_val[now]=pv;
        vis[now]=true;
        for (ne=V[now];ne;ne=ne->next)
        {
                if (vis[ne->np])
                {
                        if (S.find(path_val[ne->np] ^ path_val[now] ^ ne->val)==S.end())
                        {
                                vec[totv++]=path_val[ne->np] ^ path_val[now] ^ ne->val;
                                S.insert(vec[totv-1]);
                        }
                }else
                {
                        dfs(ne->np,pv^(ne->val));
                }
        }
}
bool cmp_v(qword x,qword y)
{
        return x>y;
}
int main()
{
        freopen("input.txt","r",stdin);
        int n,m;
        scanf("%d%d",&n,&m);
        int i,j,k,x,y;
        qword z;
        for (i=0;i<m;i++)
        {
                scanf("%d%d%lld",&x,&y,&z);
                addedge(x,y,z);
                addedge(y,x,z);
        }
        dfs(1,0);
        for (i=0;i<totv;i++)
        {
                sort(vec+i,vec+totv,cmp_v);
                totv=unique(vec+i,vec+totv)-vec;
                for (j=i+1;j<totv;j++)
                        if ((vec[j]^vec[i])<vec[j])
                                vec[j]^=vec[i];
        }
        z=path_val[n];
        for (i=0;i<totv;i++)
                if ((z^vec[i])>z)
                        z^=vec[i];
        printf("%lld\n",z);
}