2018杭电多校：Problem F. Grab The Tree

题目描述

Little Q and Little T are playing a game on a tree. There are n vertices on the tree, labeled by 1,2,...,n, connected by n−1 bidirectional edges. The i-th vertex has the value of wi.
In this game, Little Q needs to grab some vertices on the tree. He can select any number of vertices to grab, but he is not allowed to grab both vertices that are adjacent on the tree. That is, if there is an edge between x and y, he can't grab both x and y. After Q's move, Little T will grab all of the rest vertices. So when the game finishes, every vertex will be occupied by either Q or T.
The final score of each player is the bitwise XOR sum of his choosen vertices' value. The one who has the higher score will win the game. It is also possible for the game to end in a draw. Assume they all will play optimally, please write a program to predict the result.

输入

The first line of the input contains an integer T(1≤T≤20), denoting the number of test cases.
In each test case, there is one integer n(1≤n≤100000) in the first line, denoting the number of vertices.
In the next line, there are n integers w1,w2,...,wn(1≤wi≤109), denoting the value of each vertex.
For the next n−1 lines, each line contains two integers u and v, denoting a bidirectional edge between vertex u and v.

输出

For each test case, print a single line containing a word, denoting the result. If Q wins, please print Q. If T wins, please print T. And if the game ends in a draw, please print D.

样例输入

1
3
2 2 2
1 2
1 3

样例输出

Q

解题：除了异或和为0时平手，其他情况先手必胜。

#include<bits/stdc++.h>
using namespace std;
const int maxn=1e5+5;
int num[maxn];
int main()
{
    int t,len,a,b;
    scanf("%d",&t);
    while (t--){
        scanf("%d",&len);
        int ans=0,j;
        for (int i=0;i<len;i++){
            scanf("%d",&num[i]);
            ans^=num[i]; 
        } 
        for (int i=1;i<len;i++){
            scanf("%d%d",&a,&b);
        }
        if (ans==0)
        printf("D\n");
        else
        printf("Q\n");
    } 
}