Codeforces 429 A. Xor-tree

从上往下遇到第一个不相同的结点就翻转,递归就行了....

A. Xor-tree

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

Iahub is very proud of his recent discovery, propagating trees. Right now, he invented a new tree, called xor-tree. After this new revolutionary discovery, he invented a game for kids which uses xor-trees.

The game is played on a tree having n nodes, numbered from 1 to n.
Each node i has an initial value initi,
which is either 0 or 1. The root of the tree is node 1.

One can perform several (possibly, zero) operations on the tree during the game. The only available type of operation is to pick a nodex. Right after someone
has picked node x, the value of node x flips, the
values of sons of x remain the same, the values of sons of sons of x flips,
the values of sons of sons of sons of x remain the same and so on.

The goal of the game is to get each node i to have value goali,
which can also be only 0 or 1. You need to reach the goal of the game by using minimum number of operations.

Input

The first line contains an integer n (1 ≤ n ≤ 105).
Each of the next n - 1 lines contains two integers ui and vi (1 ≤ ui, vi ≤ n; ui ≠ vi)
meaning there is an edge between nodes ui and vi.

The next line contains n integer numbers, the i-th
of them corresponds to initi (initi is
either 0 or 1). The following line also contains ninteger numbers, the i-th
number corresponds to goali (goali is
either 0 or 1).

Output

In the first line output an integer number cnt, representing the minimal number of operations you perform. Each of the next cnt lines
should contain an integer xi,
representing that you pick a node xi.

Sample test(s)

input

10
2 1
3 1
4 2
5 1
6 2
7 5
8 6
9 8
10 5
1 0 1 1 0 1 0 1 0 1
1 0 1 0 0 1 1 1 0 1

output

2
4
7

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>

using namespace std;

int n,init[110000],goal[110000];
vector<int> g[110000],ans;

void dfs(int u,int fa,int c1,int c2)
{
if(c1) init[u]^=1;
if(init[u]!=goal[u])
{
c1^=1; ans.push_back(u);
}
for(int i=0;i<g[u].size();i++)
{
int v=g[u][i];
if(v==fa) continue;
dfs(v,u,c2,c1);
}
}

int main()
{
scanf("%d",&n);
for(int i=1;i<n;i++)
{
int a,b;
scanf("%d%d",&a,&b);
g[a].push_back(b);
g[b].push_back(a);
}
g[0].push_back(1);
for(int i=1;i<=n;i++)
scanf("%d",init+i);
for(int i=1;i<=n;i++)
scanf("%d",goal+i);
dfs(0,0,0,0);
printf("%d\n",(int)ans.size());
for(int i=0;i<ans.size();i++)
printf("%d\n",ans[i]);
return 0;
}