【贪心】 BZOJ 3252:攻略

  1 #include<cstdio>
  2 #include<cstring>
  3 #include<cmath>
  4 #include<algorithm>
  5 #include<vector>
  6 
  7 #define maxn 200001
  8 
  9 using namespace std;
 10 
 11 vector<int>graph[maxn];
 12 
 13 int rev[maxn],in[maxn],father[maxn],dfn[maxn],last[maxn],tot=0;
 14 
 15 long long a[maxn];
 16 
 17 bool vis[maxn];
 18 
 19 struct tr{
 20     int l,r,ps;
 21     long long num,tag;
 22 }tree[maxn*6];
 23 
 24 long long read()
 25 {
 26     long long x=0;char ch=getchar();
 27     while(ch<‘0‘||ch>‘9‘)ch=getchar();
 28     while(ch>=‘0‘&&ch<=‘9‘)x=x*10+ch-‘0‘,ch=getchar();
 29     return x;
 30 }
 31 
 32 void DFS(int poi)
 33 {
 34     dfn[poi]=++tot;
 35     rev[tot]=poi;
 36     for(int i=graph[poi].size()-1;i>=0;i--)
 37     {
 38         int u=graph[poi][i];
 39         DFS(u);
 40     }
 41     last[poi]=tot;
 42 }
 43 
 44 void psh(int poi)
 45 {
 46     if(tree[poi].tag&&tree[poi].l!=tree[poi].r)
 47     {
 48     tree[poi<<1].tag+=tree[poi].tag;
 49     tree[(poi<<1)|1].tag+=tree[poi].tag;
 50     tree[poi<<1].num+=tree[poi].tag;
 51     tree[(poi<<1)|1].num+=tree[poi].tag;
 52     tree[poi].tag=0;
 53     }
 54 }
 55 
 56 void update(int num,int l,int r,long long d)
 57 {
 58     psh(num);
 59     if(tree[num].l==l&&tree[num].r==r)
 60     {
 61         tree[num].num+=d;
 62         tree[num].tag+=d;
 63         return;
 64     }
 65     int mid=(tree[num].l+tree[num].r)>>1;
 66     if(mid>=r)update(num<<1,l,r,d);
 67     else if(l>mid)update((num<<1)|1,l,r,d);
 68     else update(num<<1,l,mid,d),update((num<<1)|1,mid+1,r,d);
 69     if(tree[num].l==tree[num].r)return;
 70     if(tree[num<<1].num>tree[(num<<1)|1].num){tree[num].num=tree[num<<1].num,tree[num].ps=tree[num<<1].ps;}
 71     if(tree[(num<<1)|1].num>=tree[num<<1].num){tree[num].num=tree[(num<<1)|1].num,tree[num].ps=tree[(num<<1)|1].ps;}
 72 }
 73 
 74 void build(int num,int l,int r)
 75 {
 76     if(l==r)
 77     {
 78         tree[num].l=tree[num].r=l;
 79         tree[num].ps=l;
 80         return;
 81     }
 82     int mid=(l+r)>>1;
 83     build(num<<1,l,mid);
 84     build((num<<1)|1,mid+1,r);
 85     tree[num].l=l,tree[num].r=r;
 86     tree[num].ps=tree[(num<<1)|1].ps;
 87 }
 88 
 89 int main()
 90 {
 91     long long ans=0;
 92     int n,k;
 93     n=read(),k=read();
 94     for(int i=1;i<=n;i++)a[i]=read();
 95     for(int i=1;i<n;i++)
 96     {
 97         int u,v;
 98     u=read();v=read();
 99     graph[u].push_back(v);
100     father[v]=u;
101     }
102     
103     father[1]=0;
104     
105     DFS(1);
106     build(1,1,n);
107     
108     for(int i=1;i<=n;i++)
109         update(1,dfn[i],last[i],a[i]);
110 
111     while(k--)
112     {
113     psh(1);
114     ans+=tree[1].num;
115     int u=rev[tree[1].ps];
116     while(u&&!vis[u])
117     {
118         vis[u]=1;
119         update(1,dfn[u],last[u],-a[u]);
120         u=father[u];
121     }
122     }
123     printf("%lld",ans);
124     return 0;
125 }