Hdu 5325 Crazy Bobo (拓扑排序)

解析：对于原树一条边(a,b)，令w[a] < w[b]​​ ，则由b向a连一条有向边. 那么，以节点u为最小权值点的最大Bobo  Set，就是走有向边能够到达u的点们构成的集合.

[code]:

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

using namespace std;
const int maxn = 5e5+5;

struct Nod{
int b,next;
void init(int b,int next){
this->b=b;this->next=next;
}
}buf[maxn*2];
int n,len,E[maxn],w[maxn],deg[maxn];
queue<int> que;
int dp[maxn];

void init(){
len = 0;
memset(E,-1,(n+1)*sizeof(int));
memset(deg,0,(n+1)*sizeof(int));
}
void add_edge(int a,int b){
if(w[a]<w[b]) swap(a,b);
buf[len].init(b,E[a]);E[a]=len++;
deg[b]++;
}
void topo(){
int i,j;
for(i = 1;i <= n;i++){
dp[i] = 1;
if(deg[i]==0){
que.push(i);
}
}
int u,v;
while(!que.empty()){
u = que.front();que.pop();
for(i = E[u];i != -1;i = buf[i].next){
v = buf[i].b;
dp[v] += dp[u];
if(--deg[v]==0) que.push(v);
}
}
printf("%d\n",*max_element(dp+1,dp+n+1));
}

int main(){
int i,j,u,v;
while(~scanf("%d",&n)){
init();
for(i = 1;i<= n;i++) scanf("%d",&w[i]);
for(i = 1;i < n;i++){
scanf("%d%d",&u,&v);
add_edge(u,v);
}
topo();
}
return 0;
}