<span>HDU5883 The Best Path（并查集+欧拉路）</span>

/* ***********************************************
Author        :devil
************************************************ */
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <map>
#include <string>
#include <cmath>
#include <stdlib.h>
#define inf 0x3f3f3f3f
#define LL long long
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define dep(i,a,b) for(int i=a;i>=b;i--)
#define ou(a) printf("%d\n",a)
#define pb push_back
#define mkp make_pair
template<class T>inline void rd(T &x){char c=getchar();x=0;while(!isdigit(c))c=getchar();while(isdigit(c)){x=x*10+c-'0';c=getchar();}}
#define IN freopen("in.txt","r",stdin);
#define OUT freopen("out.txt","w",stdout);
using namespace std;
const int mod=1e9+7;
const int N=1e5+10;
int cnt,a[N],deg[N];
int pre[N];
int fnd(int x)
{
    int r=x;
    while(pre[r]!=r) r=pre[r];
    int i=x,j;
    while(i!=r)
    {
         j=pre[i];
         pre[i]=r;
         i=j;
    }
    return r;
}
void join(int x,int y)
{
    x=fnd(x),y=fnd(y);
    if(x!=y)
    {
        pre[x]=y;
        cnt--;
    }
}
int main()
{
    int t,n,m,x,y;
    rd(t);
    while(t--)
    {
        rd(n),rd(m);
        rep(i,1,n) rd(a[i]);
        memset(deg,0,sizeof(deg));
        cnt=n;
        rep(i,1,n) pre[i]=i;
        while(m--)
        {
            rd(x),rd(y);
            join(x,y);
            deg[x]++;
            deg[y]++;
        }
        if(cnt>1)
        {
            printf("Impossible\n");
            continue;
        }
        int con=0;
        rep(i,1,n) if(deg[i]%2) con++;
        if(con!=0&&con!=2)
        {
            printf("Impossible\n");
            continue;
        }
        int ans=0;
        if(con)
        {
            rep(i,1,n) if(((deg[i]+1)/2)&1) ans^=a[i];
        }
        else
        {
            int tmp=0;
            rep(i,1,n) if((deg[i]/2)&1) tmp^=a[i];
            rep(i,1,n) ans=max(ans,tmp^a[i]);
        }
        printf("%d\n",ans);
    }
    return 0;
}