hdu5883 The Best Path（欧拉路）

题意：一个图，每一条边只能经过一次，求最大的异或和

思路：每一条边只能经过一次其实就是求是否存在欧拉路，直接判度数是否都为偶或者奇数度只有2个即可，对于度数都为偶数的起点和终点会是同一点，那么枚举一下起点就可以了，对于有两个奇数度的，考虑每一个点的贡献即可

注意：这题代码其实有问题的，只是数据水了让我混过去了，感谢评论区的漂亮大神的提醒~

真*题解： http://blog.youkuaiyun.com/f_zyj/article/details/73825643

#include<bits/stdc++.h>
using namespace std;
const int maxn = 1e5+7;
int a[maxn];
int degree[maxn];
int main()
{
	int T;
	scanf("%d",&T);
	while(T--)
	{
		memset(degree,0,sizeof(degree));
		int n,m;
		scanf("%d%d",&n,&m);
		for(int i = 1;i<=n;i++)
			scanf("%d",&a[i]);
		for(int i = 1;i<=m;i++)
		{
			int u,v;
			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;
		}
		if(cnt==0)
		{
            int ans = 0;
			for(int i = 1;i<=n;i++)
				ans = max(ans,ans^a[i]);
			printf("%d\n",ans);
		}
		else
		{
            int ans = 0;
			for(int i = 1;i<=n;i++)
			{
				degree[i]=(degree[i]+1)/2;
				if(degree[i]&1)
					ans^=a[i];
			}
			printf("%d\n",ans);
		}
	}
}

Problem Description

Alice is planning her travel route in a beautiful valley. In this valley, there are N lakes, and M rivers linking these lakes. Alice wants to start her trip from one lake, and enjoys the landscape by boat. That means she need to set up a path which go through every river exactly once. In addition, Alice has a specific number (a1,a2,...,an) for each lake. If the path she finds is P0→P1→...→Pt, the lucky number of this trip would be aP0XORaP1XOR...XORaPt. She want to make this number as large as possible. Can you help her?

 

Input

The first line of input contains an integer t, the number of test cases. t test cases follow.

For each test case, in the first line there are two positive integers N (N≤100000) and M (M≤500000), as described above. The i-th line of the next N lines contains an integer ai(∀i,0≤ai≤10000) representing the number of the i-th lake.

The i-th line of the next M lines contains two integers ui and vi representing the i-th river between the ui-th lake and vi-th lake. It is possible that ui=vi.

 

Output

For each test cases, output the largest lucky number. If it dose not have any path, output "Impossible".

 

Sample Input

2
3 2
3
4
5
1 2
2 3
4 3
1
2
3
4
1 2
2 3
2 4

 

Sample Output

2
Impossible