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\n",ans);
    return 0;
}