BZOJ 4027: [HEOI2015]兔子与樱花 贪心

现在感觉还是挺好想的. 

Code: 

#include <bits/stdc++.h>   
#define N 2000006 
#define ll long long 
#define setIO(s) freopen(s".in","r",stdin) 
using namespace std;  
vector<int>v[N];        
int n,m,edges,ans,val[N],son[N],hd[N],to[N],nex[N]; 
void add(int u,int v) 
{
    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v;     
}     
bool cmp(int i,int j) 
{
    return val[i]<val[j];       
}
void dfs(int x) 
{
    for(int i=hd[x];i;i=nex[i]) dfs(to[i]), v[x].push_back(to[i]);  
    sort(v[x].begin(),v[x].end(),cmp);      
    val[x]+=v[x].size();                     
    for(int i=0;i<v[x].size();++i) 
    {
        int cur=v[x][i];        
        if(val[cur]+val[x]-1<=m) 
        {
            val[x]+=val[cur]-1;   
            ++ans; 
        } 
        else
        {
            break;     
        }
    }
}
int main() 
{ 
    int i,j;
    // setIO("input"); 
    scanf("%d%d",&n,&m);
    for(i=1;i<=n;++i) scanf("%d",&val[i]); 
    for(i=1;i<=n;++i) 
    {
        scanf("%d",&son[i]);   
        for(j=1;j<=son[i];++j) 
        {
            int x; 
            scanf("%d",&x), add(i,x+1);   
        }   
    }
    dfs(1);    
    printf("%d
",ans);      
    return 0; 
}