POJ1655 Balancing Act

Posted 2020-08-06

题解:

树形dp求重心裸题

代码:

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define se second
#define fs first
#define ll long long
#define CLR(x) memset(x,0,sizeof x)
#define MC(x,y) memcpy(x,y,sizeof(x))  
#define SZ(x) ((int)(x).size())
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1 
#define INF 2097152
typedef pair<int,int> P;
const double eps=1e-9;
const int maxn=20000+10;
const int mod=1e9+7;

int son[maxn],vis[maxn];
int head[maxn];
int n,Siz,cnt,ans;

struct Edge{
    int to,nxt;
};

Edge edge[2*maxn];

void Init(){
    cnt=0;
    Siz=INF;
    memset(vis,0,sizeof(vis));
    memset(head,-1,sizeof(head));
}

void addedge(int u,int v){
    edge[cnt].to=v;
    edge[cnt].nxt=head[u];
    head[u]=cnt++;
}


void dfs(int u){
    vis[u]=1;
    son[u]=0;
    int tmp=0;
    for(int i=head[u];~i;i=edge[i].nxt){
        int v=edge[i].to;
        if(!vis[v]){
            dfs(v);
            son[u]+=(son[v]+1);
            tmp=max(tmp,son[v]+1);
        }
    }
    tmp=max(tmp,n-son[u]-1);
    if(tmp<Siz||(tmp==Siz&&u<ans)){
        Siz=tmp;
        ans=u;
    }
}

int main()
{
    int t,u,v;
    scanf("%d",&t);
    while(t--){
        Init();
        scanf("%d",&n);
        for(int i=1;i<=n-1;i++){
            scanf("%d%d",&u,&v);
            addedge(u,v);addedge(v,u);
        }
        dfs(1);
        printf("%d %d\n",ans,Siz);
    }
    return 0;
}