牛客练习赛32 B题 Xor Path

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define clr(a,val) memset(a,val,sizeof(a))
 4 #define RI register int
 5 #define eps 1e-6
 6 typedef long long ll;
 7 const int INF=0x3f3f3f3f;
 8 inline ll read()
 9 {
10     ll x=0,f=1;char ch=getchar();
11     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘) f=-1;ch=getchar();}
12     while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
13     return x*f;
14 }
15 const int maxn=1e6+10;
16 ll n,u,v,tot,head[maxn],val[maxn];
17 ll cnt[maxn],ans;
18 struct Edge{
19     ll u,v,nxt;
20 } edge[maxn];
21 inline void Init() {clr(head,-1);ans=0;tot=0;clr(cnt,0);}
22 inline void addedge(ll u,ll v)
23 {
24     edge[tot].u=u;
25     edge[tot].v=v;
26     edge[tot].nxt=head[u];
27     head[u]=tot++;
28 }
29 inline void dfs(ll t,ll pre)
30 {
31     cnt[t]=1; ll sum=0;
32     for(ll i=head[t];~i;i=edge[i].nxt)
33     {
34         ll v=edge[i].v;
35         if(v!=pre)
36         {
37             dfs(v,t);
38             sum+=cnt[v]*(cnt[t]-1);
39             cnt[t]+=cnt[v];
40         }
41     }
42     sum+=(cnt[t]-1)*(n-cnt[t])+n-1;
43     if(sum&1) ans^=val[t];
44 }
45 int main()
46 {
47     n=read(); Init();
48     for(ll i=0;i<n-1;++i) { u=read(),v=read();addedge(u,v);addedge(v,u);}
49     for(ll i=1;i<=n;++i) val[i]=read();
50     dfs(1,0);
51     printf("%lld\n",ans);
52     return 0;    
53 }