HDU 5883 HDU - 5883——欧拉路

注意判一下欧拉回路的情况，这种情况下需要找一个点再异或一次

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 1e5 + 10;
const int maxm = 1e6 + 10;
int T, n, m, a[maxn];
int mem, head[maxn];
struct Edge { int to, next; }edges[maxm];
void init_edges() {
    mem = 0;
    for (int i = 0; i <= n; i++) head[i] = -1;
}
void addedge(int u, int v) {
    edges[mem].to = v; edges[mem].next = head[u]; head[u] = mem++;
}
char c;
inline void input(int &x) {
    x = 0;
    while ((c = getchar()) < '0' || c > '9');
    while ('0' <= c && c <= '9') x = x * 10 + (c - '0'), c = getchar();
}
int degree[maxn];
bool vis[maxn];
void dfs(int u) {
    vis[u] = 1;
    for (int i = head[u]; ~i; i = edges[i].next) {
        int v = edges[i].to;
        if (!vis[v]) dfs(v);
    }
}
int main() {
    input(T);
    while (T--) {
        input(n); input(m);
        init_edges();
        for (int i = 0; i <= n; i++) degree[i] = 0;
        for (int i = 1; i <= n; i++) input(a[i]);
        int u, v;
        for (int i = 1; i <= m; i++) {
            input(u); input(v);
            addedge(u, v); addedge(v, u);
            degree[u]++; degree[v]++;
        }
        int cnt = 0;
        for (int i = 0; i <= n; i++) vis[i] = 0;
        for (int i = 1; i <= n; i++) if (!vis[i]) { dfs(i); cnt++; }
        int cnt_ = 0;
        for (int i = 1; i <= n; i++) if (degree[i] % 2) cnt_++;
        if (cnt > 1 || (cnt_ != 0 && cnt_ != 2)) puts("Impossible");
        else {
            int ans = 0;
            for (int i = 1; i <= n; i++) {
                if (degree[i] % 2 == 0) ans ^= (degree[i]/2)%2*a[i];
                else ans ^= (degree[i]/2+1)%2*a[i];
            }
            int temp = ans;
            if (cnt_ == 0) {
                for (int i = 1; i <= n; i++) ans = max(ans, temp ^ a[i]);
            }
            printf("%d\n", ans);
        }
    }
    return 0;
}