Codeforces Round #245 (Div. 1)??Xor-tree_html/css_WEB-ITnose

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Question meaning:
Given a tree with n nodes, 1 is the root node. The operation is to select a node x, invert the current value, the grandchild of x, and the grandchild of the grandchild. . . Negate all
Now tell the initial value of each point and the final target value of each point, and find those nodes that need to be selected when the number of operations is minimum
(1?≤?n?≤?105)

Analysis:
Points with shallow depth must be the least affected (the root node is only affected by itself), so it can be processed recursively downward from the root

const int MAXN = 110000;VI G[MAXN], ans;int now[MAXN], goal[MAXN];void dfs(int u, int fa, int a, int b){	int rev = ((now[u] ^ a) != goal[u]);	if (rev) 	{		ans.push_back(u);		a ^= 1;	}	REP(i, G[u].size())	{		int v = G[u][i];		if (v != fa)			dfs(v, u, b, a);	}}int main(){	//    freopen("in.txt", "r", stdin);	int n, a, b;	while (~RI(n))	{		FE(i, 0, n) G[i].clear();		ans.clear();		REP(i, n - 1)		{			RII(a, b);			G[a].push_back(b);			G[b].push_back(a);		}		FE(i, 1, n) RI(now[i]);		FE(i, 1, n) RI(goal[i]);		dfs(1, 0, 0, 0);		WI(ans.size());		REP(i, ans.size())			WI(ans[i]);	}	return 0;}