F-The Best Path

#include<iostream>
#include<cstdio>
#include<cstring>

using namespace std;

const int maxn = 1e5 + 10;

int n, m;
int a[maxn];
int degree[maxn];

int main()
{   
    freopen("in.txt","r",stdin);
    int t;
    scanf("%d", &t);
    while (t--) {
        memset(degree, 0, sizeof(degree));
        scanf("%d%d", &n, &m);
        for (int i = 1; i <= n; i++) 
        {
            scanf("%d", &a[i]);
        }
        int u, v;
        for (int i = 1; i <= m; i++) 
        {
            scanf("%d%d", &u, &v);
            degree[u]++;
            degree[v]++;
        }
        int cnt = 0;
        for (int i = 1; i <= n; i++) 
        {
            if (degree[i] & 1) {
                cnt++;
            }
        }
        if (cnt != 0 && cnt != 2) {
            printf("Impossible\n");
            continue;
        }
        int ans = 0;
        for (int i = 1; i <= n; i++) 
        {
            degree[i] = (degree[i] + 1) >> 1;//计算每个点经过的次数，每个点肯定都要经过而且经过的次数不一定。
            if (degree[i] & 1) //如果点经过的次数为偶数次那么异或完以后还是0，只有奇数次的点异或才有意义
            {
                ans ^= a[i];
            }
        }
        int tmp = ans;
        if (cnt == 0)//如果是欧拉回路，起点要多经过一次，所以要枚举一边所有的点作为起点找到最大值
        {
            for (int i = 1; i <= n; i++)
            {
                ans = max(ans, tmp ^ a[i]);
            }
        }
        printf("%d\n", ans);
    }
    return 0;
}