Educational Codeforces Round 27 G. Shortest Path Problem?

#include <iostream>
#include <algorithm>
#include <sstream>
#include <string>
#include <queue>
#include <cstdio>
#include <map>
#include <set>
#include <utility>
#include <stack>
#include <cstring>
#include <cmath>
#include <vector>
#include <ctime>
using namespace std;
#define pb push_back
#define sd(n) scanf("%d",&n)
#define sdd(n,m) scanf("%d%d",&n,&m)
#define sddd(n,m,k) scanf("%d%d%d",&n,&m,&k)
#define sld(n) scanf("%lld",&n)
#define sldd(n,m) scanf("%lld%lld",&n,&m)
#define slddd(n,m,k) scanf("%lld%lld%lld",&n
4000
,&m,&k)
#define sf(n) scanf("%lf",&n)
#define sff(n,m) scanf("%lf%lf",&n,&m)
#define sfff(n,m,k) scanf("%lf%lf%lf",&n,&m,&k)
#define ss(str) scanf("%s",str)
#define ans() printf("%d",ans)
#define ansn() printf("%d\n",ans)
#define anss() printf("%d ",ans)
#define lans() printf("%lld",ans)
#define lanss() printf("%lld ",ans)
#define lansn() printf("%lld\n",ans)
#define fansn() printf("%.5f\n",ans)
#define r0(i,n) for(int i=0;i<(n);++i)
#define r1(i,e) for(int i=1;i<=e;++i)
#define rn(i,e) for(int i=e;i>=1;--i)
#define rsz(i,v) for(int i=0;i<(int)v.size();++i)
#define szz(x) ((int)x.size())
#define mst(abc,bca) memset(abc,bca,sizeof abc)
#define lowbit(a) (a&(-a))
#define all(a) a.begin(),a.end()
#define pii pair<int,int>
#define pli pair<ll,int>
#define mp make_pair
#define lrt rt<<1
#define rrt rt<<1|1
#define X first
#define Y second
#define PI (acos(-1.0))
#define sqr(a) ((a)*(a))
typedef long long ll;
typedef unsigned long long ull;
const int mod = 1000000000+7;
const double eps=1e-9;
const int inf=0x3f3f3f3f;
const ll infl = 10000000000000000;
const int maxn=  100000+10;
const int maxm = 1000000+10;

int in(int &ret)
{
char c;
int sgn ;
if(c=getchar(),c==EOF)return -1;
while(c!='-'&&(c<'0'||c>'9'))c=getchar();
sgn = (c=='-')?-1:1;
ret = (c=='-')?0:(c-'0');
while(c=getchar(),c>='0'&&c<='9')ret = ret*10+(c-'0');
ret *=sgn;
return 1;
}
vector<int>base;
vector<pii>G[maxn];
int t[maxn];
bool vis[maxn];
void add(int x)
{
int sz = base.size();
for(int i=0;i<sz;++i)
{
x = min(x,x^base[i]);
}
if(x)base.pb(x);
}
void dfs(int cur,int now)
{
t[cur] = now, vis[cur]=1;
int sz = G[cur].size();
for(int i=0;i<sz;++i)
{
pii p = G[cur][i];
int to = p.X;
int w = p.Y;
if(vis[to])add(now^w^t[to]);
else dfs(to,now^w);
}
}
int main()
{
#ifdef LOCAL
freopen("input.txt","r",stdin);
//    freopen("output.txt","w",stdout);
#endif // LOCAL

//    freopen("input.txt","r",stdin);
//    freopen("output.txt","w",stdout);

int n,m;
sdd(n,m);
while(m--)
{
int u,v,w;
sddd(u,v,w);
G[u].pb(mp(v,w));
G[v].pb(mp(u,w));
}
dfs(1,0);
int sz = base.size();
for(int i=0;i<sz;++i)t
= min(t
,t
^base[i]);
int ans = t
;
ansn();

return 0;
}