[POI2009]GAS-Fire Extinguishers救火站

链接

树形+背包

#include<bits/stdc++.h>
#define re return
#define inc(i,l,r) for(int i=l;i<=r;++i)
using namespace std;
template<typename T>inline void rd(T&x)
{
    char c;bool f=0;
    while((c=getchar())<'0'||c>'9')if(c=='-')f=1;
    x=c^48;
    while((c=getchar())>='0'&&c<='9')x=x*10+(c^48);
    if(f)x=-x;
} 

#define ll long long
#define dec(i,l,r) for(int i=l;i>=r;--i)
const int maxn=100005;
ll n,s,d,hd[maxn],f[maxn][25],g[maxn][25];

struct edge{
    int to,nt;
}e[maxn<<1];
int tot;
inline void add(int x,int y)
{
    e[++tot].to=y;e[tot].nt=hd[x];hd[x]=tot;
    e[++tot].to=x;e[tot].nt=hd[y];hd[y]=tot;
}

ll ans;
inline void dfs(int x,int fa)
{
    for(int i=hd[x];i;i=e[i].nt){
        int v=e[i].to;
        if(v==fa)continue;
        dfs(v,x);
        inc(k,1,d){
            f[x][k]=min(f[x][k]+f[v][k-1],n);
            g[x][k]+=g[v][k-1];
        }
    }
    
    g[x][0]++;
    if(g[x][d]){
        int t=(g[x][d]-1)/s+1;
        f[x][0]+=min(n,s*t);
        ans+=t;
    }    
    
    inc(i,0,d){
        int j=d-i;
        ll now=min(f[x][i],g[x][j]);
        f[x][i]-=now;g[x][j]-=now;
    }
    
    inc(i,0,d-1){
        int j=d-i-1;
        ll now=min(f[x][i],g[x][j]);
        f[x][i]-=now;g[x][j]-=now;
    }
    
}

int main()
{
//    freopen("in.txt","r",stdin);
    int x,y;
    rd(n),rd(s),rd(d);
    inc(i,2,n)
    {
        rd(x),rd(y);
        add(x,y);
    }
    
    dfs(1,0);
    int sum=0;
    inc(i,0,d)
    dec(j,d,0)
        if(i+j<=d)
    {
        int now=min(f[1][i],g[1][j]);
        f[1][i]-=now,g[1][j]-=now;
    }
    inc(i,0,d)sum+=g[1][i];
    ans+=(sum?(sum-1)/s+1:0); 
    
    printf("%d",ans);
    re 0;
}