HDU 5883 The Best Path

#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<=b;++i)
#define ms(arr,a) memset(arr,a,sizeof arr)
const int maxn=1e5+5;
int w[maxn],a[maxn];
int fa[maxn];
int root(int x)
{
    int r=x;
    while(r!=fa[r])r=fa[r];
    while(x!=r)
    {
        int tmp=fa[x];
        fa[x]=r;
        x=tmp;
    }
    return r;
}
int main()
{
    //freopen("Input.txt","r",stdin);
    //freopen("Output.txt","w",stdout);
    int T;scanf("%d",&T);
    while(T--)
    {
        ms(a,0);
        int n,m;scanf("%d%d",&n,&m);
        rep(i,1,n)fa[i]=i;
        rep(i,1,n)scanf("%d",w+i);
        rep(i,1,m)
        {
            int u,v;scanf("%d%d",&u,&v);
            a[u]++;
            a[v]++;
            if(root(u)!=root(v))fa[u]=v;
        }
        int sum_graph=0;
        rep(i,1,n)
        {
            if(fa[i]==i)sum_graph++;
        }
        if(sum_graph!=1){printf("Impossible
");continue;}
        int odd=0;
        rep(i,1,n)if(a[i]&1)odd++;
        if(odd>2){printf("Impossible
");continue;}
        int ans=0;
        if(odd==2)
        {
            rep(i,1,n)
            {
                int tp=(a[i]+1)/2;
                if(tp&1)ans^=w[i];
            }
        }
        if(odd==0)
        {
            rep(i,1,n)
            {
                int tp=a[i]/2;
                if(tp&1)ans^=w[i];
            }
            int Max=ans;
            rep(i,1,n)
            {
                Max=max(Max,ans^w[i]);
            }
            ans=Max;
        }
        printf("%d
",ans);
    }
    //freopen("CON","w",stdout);
    //system("start Output.txt");
}